Feature Article /
Aug 26, 2022

A Comprehensive Glossary of Insulation Installation Terms

installation insulation terms

The below glossary of insulation terms comes from Koala Insulation of South Kansas City, which put together the reference to help professionals and homeowners alike better understand the terms surrounding the product and process.


A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z


A-SIDE: (A-Component) One component of a two-component system. For polyurethane foam and coatings, this is the Isocyanate component.

Abatement: The act of eliminating, reducing or removing something. For example, noise abatement is one of the benefits of insulation installation because the insulation helps to muffle sound.

Accelerator: A chemical additive to coating or polyurethane foam systems that is used in relatively small amounts to increase the speed of the reaction or to decrease the time required to cure or dry. 

Acoustical Treatment: Application of material that muffles or deadens sound, such as insulation.

Adhesion: The degree of attachment or bonding of one substance to another, or the degree of attachment or bonding between applications of the same substance.

Aerosol: A suspension of fine solid particles or liquid droplets in a gas. In high-pressure foam and coating applications, liquid SPF chemicals and coating materials are formed into an aerosol in the spray gun by expulsion through a nozzle.

Aggregate: Any mineral surfacing material, which may include crushed gravel, river-washed gravel or roofing granules.

Aging: The effect on materials that are exposed to an environment for an extended period of time.

Air Barrier: A material that is applied to a part of a building (such as a wall, ceiling, or sill plate), to prevent the movement of air through that part of the structure. 

Air Barrier System: The components used in building construction to create a plane of air tightness throughout the building envelope and control air leakage.

Air Leakage: The uncontrolled flow of conditioned air through gaps, cracks, or holes in a building envelope or its components.

Air Impermeable: Insulation with an air permanence at a specific thickness that is equal to or less than 0.02 L/s•m2 at 75 Pa pressure differential (0.004 ft3/ft2•min at 1.57 lb/ft2) tested in accordance with ASTM E 2178 or E 283.

Air Infiltration & Exfiltration: Air that leaks into or out of a house because it is not properly insulated or has deteriorated components such as windows and doors that are allowing for heat transfer.

Air Permeable: Insulation with an air permanence at a specific thickness that is greater than 0.02 L/s•m2 at 75 Pa pressure differential (0.004 ft3/ft2•min at 1.57 lb/ft2) tested in accordance with ASTM E 2178 or E 283.

Air Purifying Respirator (APR): Respirators that consist of a facemask and an air purifying device, which is either attached directly to the mask or carried on a body harness and connected to the mask via a breathing hose. APRs selectively remove specific airborne contaminants (particulate, vapors, fumes, and gas) from ambient air by filtration, adsorption, or chemical reactions. Filtering cartridges are removed and replaced at the end of their useful service life. APRs can be either full face or half mask varieties.

Air Sealing: The process of using materials such as caulk, foam, or other insulation materials to seal up holes, gaps and cracks to prevent air leakage and heat transfer and make a building more energy efficient.

Aliphatic (Polyurethane): A type of polyurethane that does not contain carbon atoms arranged in aromatic (benzene) ring structures. As compared to aromatic (polyurethane), coatings based on aliphatic polyurethane have superior resistance to UV weathering, and better color and gloss retention.

Alligatoring: Pattern cracking of a coating or mastic, so called because of its resemblance to the pattern of alligator skin.

Ambient Temperature: The temperature of the air, as measured by a thermometer, in a given location.

Amine Catalyst: A broad range of nitrogen-based compounds that are used to promote blowing and curing reactions in polyurethanes. An amine catalyst is typically contained in the B-side, or resin, of a two-component polyurethane system.

Anti-Sweat Coating: A substance that prevents or reduces condensation when applied to a surface.

Application Rate: The quantity (mass, volume, or thickness) of material applied per unit area.

Application Temperature Limits: The temperature range at which sealants, adhesives and finishes can be applied without damaging the material's integrity with exposure to heat or cold.

Area Divider: A raised, flashed assembly (typically a single-wood or double-wood member attached to a wood base plate) that is anchored to the roof deck. It is used to relieve thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas (sometimes between expansion joints). An area divider may be used to facilitate the installation of tapered insulation. 

Aromatic (Polyurethane): A type of polyurethane that contains some carbon atoms arranged in aromatic (benzene) ring structures. As compared to aliphatic (polyurethane), coatings based on aromatic polyurethane are usually tougher, but have less resistance to UV weathering, and less color and gloss retention.

Aromatic Solvents: Hydrocarbon solvents composed of organic compounds, which contain an unsaturated ring of carbon atoms, including benzene, xylene, toluene, and their derivatives.

Asbestos: A highly carcinogenic, naturally occurring mineral that was used extensively in homes and commercial properties before it was banned in the 1980s, including as insulation. Asbestos must be removed from buildings by an asbestos abatement professional.

Atomization: The breakup of liquid or fluid into spray when forced through a small opening or orifice at high pressure.

Attenuation: Increasing sound separation between two areas by limiting noise propagation, such as the muffling effect of insulation.

Attic—Vented: An unfinished space between the ceiling assembly of the top story and the roof assembly that has openings to the outside adequate to promote natural or mechanical air exchange.

Attic—Unvented: An unfinished space between the ceiling assembly of the top story and the roof assembly that has no openings to the outside adequate to promote natural or mechanical air exchange.


B-Side (B-Component): One component of a two-component system. For polyurethane foam and coatings, this is the resin component.

Back Rolling: Rolling a wet coating behind a spray or roller application to ensure better coverage on rough surfaces.

Baffles: Small pieces of plastic or cardboard that are inserted between rafters and near soffit vents to allow air to flow over top of the insulation and ensure proper attic ventilation.  

Bands: Straps of material used to fasten insulation or insulation jackets in place.

Base Coat: The first coat of a multi-coat system. This should be applied the same day as the SPF. 

Batt InsulationThick, semi-rigid, rectangular pads of insulation, usually made of fiberglass, that are pieced together to provide full coverage for the space that is being insulated. Batts may or may not come with a vapor barrier.

Binder: Also referred to as thermal setting resin, it is an additive in insulation materials that bonds fibers together and helps batts and blanket insulation retain their shape.

Blanket Insulation: A flat, semi-flexible insulation material that comes in large sheets, primarily intended for use in particularly large areas.

Blister: An uplifting of coating or polyurethane foam caused by an enclosed pocket of gas or liquid trapped between coating passes, foam and coating, foam and substrate, or within the foam itself. Caused by the delamination of one or two components in an insulation or roofing system.

Blowhole: A hole in the polyurethane foam surface and/or coating surface about 1 mm in diameter (the size of a ballpoint pen tip).

Blowing Agent: A chemical additive formulated into either the A-side or B-side of the system, which creates bubbles that are trapped in the polyurethane as it solidifies to form foam cells. The gas produced from the blowing agent contributes to more than 97% of the volume of polyurethane foam. The blowing agent can be physical or reactive in nature. The physical blowing agents (e.g., liquid fluorocarbon) vaporize with the heat of the polyurethane reaction. The reactive blowing agents (e.g., water) react with one of the other chemicals in the formulation to produce a gas during the reaction (e.g., water and isocyanate yields carbon dioxide).

Blown-In Insulation: Small, loose clumps of fiberglass, cellulose or other materials that are "blown in" to the space that needs insulating with a blower machine and settle onto all surfaces to form an insulating layer.

Board-Foot: A volume measurement of materials such as SPF insulation, board-stock insulation, and lumber. One board-foot equals a volume of 12 in. by 12 in. by 1 in. Abbreviated bd•ft (1 bd•ft = 1/12 cubic ft = 0.00236 m3).

Bond—Chemical:  Adhesion between surfaces, usually of similar materials, resulting from a chemical reaction or cross-linking of polymer chains.

Bond—Mechanical: Adhesion between surfaces resulting from interfacial forces or a physical interlocking.

Bonding Time: The length of curing or settling time required for an adhesive to reach its full bonding strength.

British Thermal Unit (BTU or Btu): A unit of measurement that represents how much heat is needed to raise the temperature of one pound of water by one degree Fahrenheit.

Building Code: A set of rules that establish the minimum acceptable levels of safety for constructed structures. Building codes also provide minimum standards for the energy consumption of structures. In the United States, model codes are developed and published by the INTERNATIONAL CODE COUNCIL (ICC) and the NATIONAL FIRE PROTECTION ASSOCIATION (NFPA). Model codes acquire legal standing when adopted by state or local authorities. 

Building Envelope: The exterior shell of a building, which provides structural integrity and control of heat, air, and moisture.

Building Science: Involves the application of basic science knowledge and analysis procedures to the design of buildings. There is special knowledge and experience required, and such expertise is also beneficial in determining how to correct problems in existing buildings and to explain what went wrong in the event of problems.

Butyl Coating: An elastomeric coating system derived from polymerized isobutylene. Butyl coatings are characterized by low water vapor permeability.


C-Value: A measure of thermal conductance that represents the time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces. A lower C-value indicates more effective insulating material.

Cant: A beveling of polyurethane foam at a right-angle joint for strength and water runoff. 

Capillary Action (Capillarity): The movement of liquid in the interstices of insulation or other porous material as a result of surface tension.

Catalyst: An ingredient in a coating or polyurethane foam system that initiates a chemical reaction or increases the rate of a chemical reaction.

Caulk: A flexible sealing compound, often made from acrylic or silicone, that is used to fill and seal gaps in buildings to prevent heat transfer, along with stopping moisture, dust, insects and other elements from passing through the gap or hole.

Caulking: The act of applying caulk.

Cavitation: The vaporization of a liquid under the suction force of a pump. Usually due to inadequate flow to a pump, the vaporization can create voids within the pump or the pump supply line. In polyurethane foam spray pumps, cavitation will result in off-ratio foam.

Cavity Wall: An exterior wall, usually of masonry, consisting of an outer and inner wythe separated by a continuous air space.

Cellular: Describes a composition of plastic or rubber with relative density decreased by the presence of cells dispersed throughout its mass. In closed cell materials, the cells are predominantly separate from each other. In open cell materials, the cells are predominantly interconnected.

Cellulose: A material used for insulation that is made of a mixture of recycled paper, recycled denim and sometimes other materials. Cellulose is typically treated with flame-retardant and pest repellent chemicals.

Chemical Resistance: The ability of a material or item to withstand the effects of acids, alkalis and salts, and compounds made with them.

Centipoise (CPS): A unit of measure of absolute viscosity. (Note: The viscosity of water is 1 cps at 20°C [68°F]. The lower the number, the less the viscosity.)

Chalking: The formation of a powdery substance due to weathering on a coated surface.

Checking:  A defect in a coated surface characterized by the appearance of fine fissures in all directions. Designated as “surface checking” if superficial or “through checking” if extending deeply into the coating or to an adjoining surface. 

Chemical Resistance: The ability to withstand contact with specified chemicals without a significant change in properties.

Coarse Orange Peel Surface Texture: A surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is acceptable for receiving a protective coating because of the roundness of the nodules and valleys. This surface requires at least 25% additional material.

Coating: A layer of material applied over a surface for protection or decoration. Coatings for polyurethane foam are liquids, semi-liquids, or mastics; are spray, roller, or brush applied; and are elastomeric.

Cobwebbing: Production of fine filaments instead of the normal atomized particles when some coatings are sprayed.

Coefficient of Expansion or Contraction: The ratio of an increase or decrease in size, area or volume of a material or object per one degree rise in temperature of that material or object.

Cohesion: The degree of internal bonding of one substance to itself.

Cold-Applied: Capable of being applied without heating as contrasted to hot-applied. Cold-applied products are furnished in a liquid state, whereas hot-applied products are furnished as solids that must be heated to liquefy them

Cold Attic Insulation: When insulation is placed on the "floor" of an attic space (or the upper side of the top story ceiling), leaving the attic itself cold and uninsulated and preventing heat transfer between the attic and uppermost habitable story of the building.

Colloidal Dispersion: A mixture wherein a finely divided material is uniformly distributed within a liquid. Latex emulsion is a colloidal dispersion of resin in water.

Color Stability: Something’s ability to retain its original color without significant change over time.

Combustible: Capable of burning.

Compatible Materials: Two or more substances that can be mixed, blended, or attached without separating, reacting, or affecting the materials adversely.

Condensation: Droplets formed when water vapor in the air condenses on a cool surface. This often occurs on glass surfaces such as windows, and it can affect wood trim if it is excessive or frequent.

Conditioned Space: An enclosed, indoor space where the air temperature is regulated to be either cooler or warmer than the air outside in order to increase indoor comfort levels.

Conditioning: The exposure of a material to the influence of a prescribed atmosphere and/or temperature for a stipulated period of time or until a stipulated relation is reached between the material and atmosphere.

Continuous Insulation (CI): Insulation that is continuous across all structural members without any thermal bridges other than fasteners and service openings. It is installed on the interior or exterior and is integral to any opaque surface of the building envelope.

Coping: The covering at the top of a wall or parapet designed to shed water.

Copolymer: A polymer consisting of molecules containing large numbers of units of two or more chemically different types in irregular sequence.

Coverage: The unit quantity of material necessary to apply to achieve a desired thickness. Usually expressed in square meter per liter (square feet per gallon) or liters per square meter (gallons per hundred square feet). 

Crawlspace—Vented: A low space beneath the floor of a building, giving workers access for the service of utilities, which is ventilated to the exterior of the building envelope. Insulation is typically installed in the crawlspace overhead (beneath the floor of the building).

Crawlspace—Unvented: A low space beneath the floor of a building, giving workers access for the service of utilities, which is not ventilated to the exterior of the building envelope. Insulation is typically installed in the crawlspace walls in this case. (Also known as a “conditioned crawlspace.”) 

Crazing (Craze Cracks): Fine, random cracks forming a network on the surface of a coating or film.

Cream Time: After mixing two SPF-forming components, cream time occurs when the mixture changes from a clear dark-colored liquid to an opaque light-colored liquid. The cream time represents the onset of the rise of the foam.

Creep: (1) The permanent deformation of a material caused by slow movement over time resulting from thermal or load stresses. (2) Lateral movement of expanding foam.

Cross Hatch: An application method for liquid applied materials whereby successive layers or passes are applied at 90-degree angles to the previous application.

Crossover: An undesirable mixing of isocyanate and resin components as a result of unbalanced pressures at the spray gun. May result in an equipment blockage.

Cure: The completeness of the chemical reaction of foam insulation installation. At substantial completion, the foam should have near the maximum physical properties attainable for the particular formulation used. Cure is not directly related to levels of product emissions during or after SPF application.

Curing Agent: An agent in a coating or adhesive that increases the rate of cure.

Curing Time: The length of time required for a product to reach its finished form via chemical reaction. For example, caulk needs a certain amount of curing time to harden and set.

Curtain Wall: A lightweight exterior wall system supporting no more than its own weight, the roof and floors being carried by an independent structural framework.


Deck: The structural surface to which a roofing or waterproofing system is applied. Spray polyurethane foam may be applied to decks on the exterior side as an insulated roofing system or to the interior side as an insulation system.

Delamination:  When a material fractures into separate constituent layers.

Desiccant: A substance that attracts water molecules from the surrounding environment through absorption. Typically used to dry compressed air or to dry makeup air entering chemical storage containers. 

Dew Point: The atmospheric temperature that air must be cooled to in order to condense and form water droplets. The exact temperature varies according to humidity and pressure.

Diffusion: The process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration, typically through or across a membrane (for example, water vapor diffusing from a humid bathroom into the bathroom walls, resulting in moisture in the wall assembly).

Diisocyanate: An organic chemical compound having two reactive isocyanate (-N=C=O) groups used in the production of polyurethane foams and polyurethane coatings.

Discoloration: Any change in an object or material’s original color.

Draftstop: A material, device, or structure installed to restrict the movement of air and smoke within the open spaces of concealed areas of building components, such as crawlspaces, floor/ceiling assemblies, roof/ceiling assemblies, and attics.

Drying Time: The time required for the loss of volatile components so that the material will become tack-free and no longer be adversely affected by weather conditions, such as dew, rain, or freezing.


Economic Thickness: There is an optimal level of economic thickness for insulation—which varies according to the local climate, what is being insulated and other factors—that will offer the best exchange of insulating value versus energy cost savings. The cost of increasing the R-value of insulation past that economic thickness point can not be recovered through diminishing energy savings returns.

Elongated Cells:  Excessively large cells in foam or coating, generally caused by off-ratio materials, moisture contamination, or excessive heat.

Energy Star: A program that is jointly operated by the U.S. Department of Energy and the U.S. Environmental Protection Agency to rate the energy efficiency of buildings and individual components or products such as doors, appliances and insulation.

Epoxy Resin: Plastics, adhesives and other materials or substances that are made from polymerized epoxides.

Exothermic Reaction: A chemical reaction that produces heat. SPF and certain coatings are the product of exothermic reactions.

Expansion Joint: A joint designed to accommodate movement in the structure or components of the system due to thermal or stress-load variation. 


Fast-Set: A term applied to a coating to indicate a faster curing time versus a standard version of the generic coating. In polyurethane and polyurea coatings, this is generally indicative of cure times in the range of a few seconds to a few minutes, or coatings that must be sprayed with plural component equipment. In acrylic coatings, this is generally indicative of a 1–3 hour cure schedule versus a 2–5 hour cure schedule at 75°F.

Feathered Edge: The thin tapered outside edge of a polyurethane foam pass.

Fiberglass: A type of insulating material made from extremely fine, hair-like strands of glass. It is resistant to heat and fire, making it a popular choice for insulating residential and commercial buildings.

Filler: A relatively inert ingredient added to coating or polyurethane foam formulations to modify their physical characteristics. 

Film Thickness: The thickness of a membrane or coating. Wet-film thickness is the thickness of a coating as applied; dry-film thickness is the thickness after curing. Film thickness is usually expressed in mm or mils (thousandths of an inch).

Fire Resistance: The ability of a material or item to withstand fire and/or block it from spreading to new areas.

Fireblocking:  Building materials or structures designed, approved, and installed to resist the free passage of flame to other areas of a building through concealed spaces.

Firestop: A material, device, or structure installed to resist the passage of flame and heat through openings in a protective membrane in order to accommodate cables, cable trays, conduit, tubing, pipes, or similar items.

Flame Retardant: A chemical compound additive that raises the flash point of a material such as insulation, giving it greater fire resistance.

Flammable: Materials, objects, liquids or gasses that are capable of being set on fire. Flammable and inflammable have the same meaning.

Flash Point: The temperature at which a material combusts when exposed to heat.

Flexibility: A property of materials or objects that allows them to be bent (flexed) without loss of strength or integrity.

Fogging: Condensation that accumulates in the space between glass panes in double-glazed windows when they lose their argon gas fill.

Forced Convection: A mechanism or heat transfer process in which fluid motion is influenced by external factors.

Froth Pack: Pressurized containers of polyurethane foam components.


Hardness: Ability of a coating film, as distinct from its substrate, to resist cutting, indentation, or penetration by a hard object.

Heat Aging: Controlled exposure of materials to elevated temperatures for a period of time.

Heat Flow Rate: The amount of thermal energy that can be transferred per unit of time in some types of materials, typically measured in watt or joules per second.

Heat Flux: The rate of heat transfer per unit area. Usually used to describe the rate of radiant heat transfer. Units are W/m2 (Btu/ft2•hr).

Heat Gain: The transfer of thermal energy from outside a building to inside via radiant energy such as sunlight.

Heat Loss: The total transfer of heat from inside a building to outside through walls, windows, doors, and other building components, measured in kW or BTU.

Heat Sink: A cold substrate that absorbs the SPF exothermic heat, slowing down the reaction and/or rise of the polyurethane foam or coating

Heat Transfer: The natural process in which thermal energy attempts to move from a warm area, such as inside a house, to a cooler area such as the outdoors.

Hertz (Hz): A unit of frequency measurement that is defined as one cycle per second. It is commonly used to measure sine waves and musical tones, along with other frequencies.

Hiding Power: The ability of a coating to hide or obscure a surface to which it has been uniformly applied.

Holidays: A slang term for insulation application defects whereby small areas are left uncoated.

Home Energy Rating System (HERS):  A rating system for residential energy efficiency developed by EnergyStar and RESNET (Residential Energy Services Network). Through a comprehensive design review and analysis, it incorporates HVAC, building enclosure, and orientation, as well as appliance and lighting selection. A HERS score of 0 indicates a net zero- energy home, while a HERS score of 100 represents the energy consumption of a home built to the 2003 IECC model energy code. A maximum HERS score of 70 is required for a home to be EnergyStar compliant.

Humidity: A measure of the level of water vapor in the atmosphere or inside an enclosed space.

Hybrid Insulation: A combination of insulation types typically arranged so the SPF insulation acts as an air barrier and/or a vapor retarder, and the other insulation type contributes by adding R-VALUE.


I-CODES®: The set of model building codes promulgated by the International Code Council (ICC). The I-Codes include the International Residential Code (IRC), the International Building Code (IBC), the International Energy Conservation Code (IECC), the International Mechanical Code, and others.

Ignition Barrier: A building-code–permitted protective covering applied over foam plastic insulations, including SPF in attics and crawlspaces, to increase the time before the foam plastic becomes involved in a fire. Ignition barriers do not provide as much fire protection as thermal barriers. The building code restricts the use of ignition barriers to attics and crawlspaces of limited access (check the local building code for exact requirements).

Impact Resistance: The ability of an object or material such as insulation to withstand physical or mechanical abuse.

Impingement Mixing: A process of mixing in which multiple liquid streams are forced toward one another at a high velocity, producing very thorough mixing in a short period of time.

Infra-Red Thermography: Photography in the infra-red wavelength wherein the temperature differences of objects and surfaces can be readily distinguished. Infra-red thermography is frequently used to (1) identify sources of heat loss or gain that affect building energy efficiency; (2) identify sections of building assemblies containing moisture; and (3) identify electrical or mechanical components that are overheating.

Interlaminar Adhesion: Adhesion between polyurethane foam passes or coating passes.

Intumescent Coating: Coatings that are formulated to swell and char when exposed to heat. When applied to a combustible (or non-combustible) substrate, this “swollen char” is designed to insulate the substrate from the heat source, thus reducing the potential for fire and/or increasing the time before the substrate becomes involved in a fire.

Isocyanate (ISO): A highly reactive organic chemical containing one or more isocyanate (N=C=O) groups. A basic component in polyurethane foam chemical systems and some polyurethane coating systems.

Isocyanurate: Also referred to as PIR, polyiso, or polyisocyanurate, isocyanurate is essentially a modified polyurethane (PUR) foam. The proportion of methylene diphenyl diisocyanate (MDI) is higher than for PUR and instead of a polyether polyol resin, a polyester derived polyol is used in the reaction. Catalysts, blowing agents, and additives used in PIR foam formulations also differ from those used in PUR. Isocyanurates are generally manufactured in a factory into boardstock form, and are used in exterior roofing and sheathing applications. The thermal performance of isocyanurate or PIR boardstock foams is comparable to medium-density closed cell SPF.

Insulating Glass Unit (IGU): A double-paned window with two (or sometimes more) panes of glass separated by a spacer and sealed at the edges. It keeps houses warmer during winter and cooler during summer by resisting heat transfer.

Insulation Density: A measure of how many fibers there are in a given area such as a square inch of insulation material. Denser insulation is usually more effective.

Insulation Removal: The process of removing insulation from a building or a specific area of a building, usually because it has become damaged or is too old and needs to be replaced.


K-Value (K-Factor): A measure of thermal conductivity showing how many BTUs of heat pass through one square foot of a homogeneous substance. Expressed as W/m2•K (Btu•in./hr•ft2•F). R-value is equal to the thickness of the material divided by the k-factor (R = x/k where x = thickness).

Knit Line: A high-density skin formed between one lift or pass of foam and another. Synonymous with lift line. 


Lacing: The process of securing or joining insulation materials together or to an anchor point with hooks, wires, cords and similar materials.

Life-Cycle Assessment (Life-Cycle Analysis, LCA): An accounting and evaluation of the environmental aspects and potential impacts of materials, products, assemblies, or buildings throughout their life, from raw material acquisition through manufacturing, construction, use, operation, demolition, and disposal.

Life-Cycle Inventory (Life-Cycle Inventory Analysis, LCI, LCIA): The identification and quantification of energy, resource usage, and environmental emissions for a particular product, process, or activity.

Lift: The sprayed polyurethane foam resulting from tying together the perimeter of adjacent passes of foam in a specific area. A lift is defined by its thickness. Multiple lifts over the same area may be needed to achieve the final foam thickness. For example, a one inch lift of foam can be installed over a 20 x 20 ft area, and then a second lift of foam 1.5 inch thick can be installed to the same area to create a final installed thickness of 2.5 inches.

Loose-Fill Insulation: Similar to blown-in insulation, this material comes in loose clumps or smaller particles and can be blown-in, poured or hand-placed.

Low-Density SPF (Open Cell SPF, ocSPF): A type of SPF expanded with reactive blowing agents to yield a semi-rigid cellular structure and a density between 8–22 kg/m3 (0.4 and 1.4 lb/ft3).

Low-Temperature Flexibility: The ability of a membrane or another material to remain flexible (resist cracking when flexed), after the membrane or material has been cooled to a low temperature.


Man-Made Vitreous Fibers (MMVF): Glassy, non-crystalline, made-made materials such as fiberglass and mineral wool.

Mastic: A coating material of relatively thick consistency.

Material Safety Data Sheet (MSDS): A standard formatted information sheet prepared by a material manufacturer that describes the potential hazards, physical properties, and procedures for the safe use of a material.

Mechanical Damage: Breaks or punctures to insulation and coating systems as a result of impact or abrasion.

Medium-Density SPF (Closed Cell SPF, ccSPF): A type of SPF expanded with nonreactive blowing agents to yield a rigid cellular structure. It is characterized by a predominance of closed cells and a density between 1.5–2.5 lb./ft3.

Membrane: A layer of material that acts to prevent the passage of a substance. Membranes may restrict the passage of air, liquid water, or water vapor. Some membranes allow the passage of some substances, while excluding others.

Membrane Reinforcement: Fabrics or fibers embedded in mastic or coating to provide strength and impact resistance.

Methylene Diphenyl Diisocyanate (MDI): Component-A in SPF. An organic chemical compound having two reactive isocyanate (N=C=O) groups. It is mixed with the B-component to form polyurethane.

MIL: One-thousandth of an inch; 0.001 in. (0.025 mm). A unit used to measure coating thickness.

Mineral Wool: A fibrous insulating material that looks similar to matted wool but is composed of inorganic minerals such as rock slag and ceramic.

Mist Coat: A very thin sprayed coat.

Mold and Mildew Resistance: The ability of a material or object to prevent mold and mildew from growing on it.

Monolithic: Formed from or composed of a single material; seamless. 

Mud-Cracking: The defect in an applied coating or mastic when it cracks into large segments or shrinks (also called alligatoring). When the action is fine and incomplete, it is usually referred to as “checking.”

Multiple Coat: Two or more layers of coating applied to a substrate.


Net Zero Energy: A building with net zero energy consumption creates the same amount of renewable energy on-site that it uses to operate.

Noise Reduction Coefficient (NRC): A representation of the amount of sound energy absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection (strong echo), and an NRC of 1 indicates perfect absorption (lack of echo).

Non-Breathing Membrane: A membrane material that has a significantly greater resistance to the diffusion of water vapor than the other materials with which it is used.

Non-Flammable: Not easily ignited and will not burn rapidly if ignited. The material may still burn and be considered combustible. OSHA defines a flammable liquid as any liquid having a flashpoint below 100°F (37.8°C).


Off-Ratio Foam: An off-ratio foam is caused by a deficiency of one of the component chemicals (A- or B-side) during application. The reaction of an off-ratio foam is readily visible to a trained SPF applicator. Off-ratio foam will negatively affect SPF yield, performance, and worker safety.

Orange Peel Surface Texture: The surface texture of SPF, which exhibits a fine granular texture and is compared to the exterior skin of an orange. This surface is considered acceptable for receiving a protective coating. This surface requires at least 10% additional coating material.

Orifice: An opening or aperture. The opening in the tip of a spray gun.

Outgassing: The slow release of a gas that was trapped, frozen, absorbed, or adsorbed in some material. Sometimes called “off-gassing,” particularly when in reference to indoor air quality.

Overspray:  (1) Airborne spray loss of polyurethane foam or coatings. (2) Undesirable depositions of airborne spray loss.

Overspray Surface Texture: A linear coarse textured pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and is unacceptable for proper coating coverage and protection if severe.


Parapet:  A wall or top portion of a wall extending above an attached horizontal surface such as a roof, terrace, or deck; often used to provide a safety barrier at a roof edge.

Pass: The volume of coating or polyurethane foam applied by moving the gun from side to side and moving away from fresh material in a single continuous application. A pass is defined by its width, length and thickness. Foam passes sprayed and tied together along their adjacent edges to cover a larger area are called a lift of foam.

Pass Lines: Pass lines are created when the end of a pass of foam or coating ties into an adjacent pass. The overlapping of the polyurethane foam or coating can be seen typically as a darker color than the middle of the pass. Foam at the pass lines typically contain thinner lifts than the middle of the foam pass as the applicator tapers the foam to uniformly tie the foam passes together.

Patching: Restoring or repairing damaged insulation materials without removing the entire installation.

PCF: Pounds per cubic foot or lb/ft3. A measure of density.

Peeling: Top-coating film inadequately bonded with undercoats resulting in partial delamination or detachment of final coat.

Penetration:  (1) Any object, such as vent pipes, electrical conduit, ducts, structural supports elements, etc., passing through a roof, wall, floor, or other building assembly. (2) Any hole or opening in a building assembly that would allow the passage of air, water, or other fluids.

Perm: A unit of water vapor permeance defined as 1 grain of water vapor per square foot per hour per inch of mercury water vapor pressure difference (1 in. of mercury = 0.49 psi). Perm = 1 grain/ft2•hr•in. Hg. The SI unit for permeance is ng/s•m2•Pa (1 perm = 57.4 ng/s•m2•Pa).

Perm Rating: The permeance of a material. Breather materials have relatively high perm ratings, vapor retarders have relatively low perm ratings, and vapor barriers have essentially zero (negligible) perm ratings.

Permeability—Air: The rate at which air will diffuse through a unit area of material induced by a unit differential in air pressure. Air permeability is generally used as a descriptive term and specific values are not usually reported.

Permeability—Water Vapor: The rate at which water vapor will diffuse through a unit thickness and area of material, induced by a unit differential in water vapor pressure. Permeability values are related to a common thickness and can be used to compare various materials. Units are usually grains•in./ft2•hr•in Hg or perm•in. SI unit for permeability is ng/s•m•Pa (1 perm•in = 1.46 ng/s•m•Pa).

Permeance—Air: The rate at which air can diffuse or leak through a unit area of material induced by a specific pressure differential, for example, 75 Pa or 1.57 lb/ft2. ASTM E 2178 and ASTM E 283 are the test methods used to measure air permeance. Units are L/s•m2 (ft3/min•ft2) with pressure reported as Pa (lb/ft2).

Permeance—Water Vapor: The rate at which water vapor will diffuse through a unit area of material induced by a unit differential in water vapor pressure. Permeance values are reported for specific thicknesses (usually recommended application thickness). Units are usually grains/ft2•hr•in Hg or perm. SI unit for permeance is ng/s•m2•Pa (1 perm = 57.4 ng/s•m2•Pa).

Personal Protective Equipment (PPE): Includes all protective equipment and supplies designed to protect employees from serious workplace injuries or illnesses resulting from contact with chemical, radiological, physical, electrical, mechanical, or other workplace hazards. Besides face shields, safety glasses, hard hats, and safety shoes, PPE includes a variety of devices and garments, such as goggles, coveralls, gloves, vests, earplugs, and respirators. 

Personnel Protection: Insulation that is specifically for the purpose of reducing surface heat or cold levels that are capable of harming humans. 

Picture Framing: Outlining the perimeter of a stud wall cavity with SPF prior to filling the center.

Pinhole: A tiny hole. When associated with insulation, it typically refers to a tiny hole in a vapor barrier or coating that reduces its ability to prevent heat transfer or block moisture incursion.

Polyethylene: Durable, flexible synthetic resin that is manufactured by polymerizing ethylene and is typically used for plastic bags, takeout containers and other similar items, as well as insulation.

Polymer: A substance consisting of high-molecular-weight chemical compounds characterized by chains of repeating simpler units.

Polymeric MDI (p-MID):  Isocyanate compounds wherein the molecules contain more than two functional -NCO groups.

Polyol: A high-weight molecule that contains hydroxyl groups (-OH), typically at the terminal position on the molecular chain. Polyol is a primary ingredient in the B-side or resin of the two-component polyurethane system. After reaction with MDI (A-side), the polyol becomes part of the polyurethane polymer.

Polyurethanes: Polyol and MDI react to form polyurethane. When this reaction occurs multiple times, a polyurethane molecule is created. Many end-use products are created using polyurethane chemistry, including rigid and flexible foams, rigid or flexible coatings, elastomers, and structural materials.

Polyurethane Coatings: A one- or two-part coating that contains polyisocyanate monomer and a hydroxyl containing resin, which react during cure to form a polyurethane elastomer.

Polyvinyl Chloride (PVC): A plastic material that comes in both flexible and rigid forms.

Popcorn Surface Texture: The surface exhibits texture of SPF where valleys form sharp angles. This surface is unacceptable for coating application. Also termed “treebark surface texture.” 

Post Expansion: A characteristic of some single-component SPFs wherein additional expansion occurs after the initial application and froth expansion. Post expansion is due mainly to the chemical curing process.

Pour Foam: A polyurethane foam system, with a slower reactivity profile (relative to SPF), designed for pouring or injection into confined spaces such as a mold, panel, or concrete blocks. 

Powered-Air Purifying Respirator: A type of air purifying respirator which consists of a powered fan that forces incoming air through one or more filters for delivery to the user for breathing. The fan and filters may be carried by the user or, with some units, the air is fed to the user via tubing while the fan and filters are remotely mounted.

Primer: The first layer of coating applied to a surface to improve the adhesion of subsequently applied materials or to inhibit corrosion.

Propellant: Liquified or compressed gas formulated into single-component SPF or two-component froth packs used to expel the SPF ingredients from its containers. The propellant also functions as a blowing agent. 

Proportioner: The basic pumping unit for spraying polyurethane foam or two-component coating systems. Consists of two positive displacement pumps designed to dispense two components at a precisely controlled ratio.

PSI: Pounds per square inch (lb/in2).

Psychrometer:  (1) A device for measuring ambient humidity by employing a dry-bulb thermometer and a wet-bulb thermometer. (2) An electronic device for measuring ambient temperature and humidity.

Psychrometric Chart: A diagram relating the properties of humid air with temperature.

Purge: To cleanse or remove liquid materials from equipment or hoses. 


R-Value: A measure of the effective heat resistance and thermal performance of insulating material. Approximate R-value is generally expressed per inch of thickness. There are a number of factors that influence R-value, including the types, densities and thicknesses of the materials. A higher R-value indicates insulation that is more effective at preventing heat transfer.

Radiant Barriers: Typically in the form of a single highly reflective sheet or coating (e.g., aluminum foil or metallized mylar), radiant barriers are applied as a component of the building enclosure to inhibit heat transfer by thermal radiation. They do not provide resistance to heat transfer by conduction or convection.

Recycle Content: The proportion of material (typically percentage by weight) in an end-use product that contains previously used materials. Recycle content can be further classified as “post-industrial” or “post-consumer.” The former refers to re-use of by-product materials that are created during the manufacturing process, while the latter refers to waste materials that come from the consumer sector.

Reflectance (Reflectivity): The fraction of incident radiation (usually the visible spectrum of sunlight) that is scattered (i.e., not absorbed or transmitted) by a surface. Reflectance is expressed as a number between 0–1 or as a percentage between 0%–100%. Cool roofs and reflective coatings have high reflectance values. 

Reflective Insulation: Similar to radiant barriers, reflective insulations are made from multiple sheets of highly reflective film that inhibit heat transfer by radiation. Multiple sheets of the reflective film are formed to create thin air pockets that can reduce heat transfer by conduction and convection in certain applications. Examples of reflective insulation would be a metalized bubble-wrap material or foil panels that unfold or deploy into a sheet with integral air compartments.

Reglet:  (1) An interlocking two-part flashing between a wall or other vertical surface and a roof. (2) A sheet metal clamp or receiver attached to a wall to which a counterflashing may be affixed. (3) A groove in a vertical surface to which a counterflashing may be affixed.

Relative Humidity: : The ratio of absolute humidity to saturation humidity, expressed as a percentage.

Resin:  (1) B-Component in SPF. This component contains a polyol, catalyst, blowing agent, fire retardant, and surfactants. It is mixed with the A-component to form polyurethane. (2) General term applied to a wide variety of more or less transparent and fusible products, which may be natural or synthetic. Higher molecular weight synthetic resins are referred to as polymers. (3) Any polymer that is a basic material for coatings and plastics.

Respirator: A device designed to protect the wearer from inhaling harmful dusts, fumes, vapors, and/or gas. Respirators come in a wide range of types and sizes. There are two main categories: (1) the air purifying respirator, which forces contaminated air through a filtering element; and (2) the air- supplied respirator, in which an alternate supply of fresh air is delivered. Within each category, different techniques are employed to reduce or eliminate noxious airborne contaminants. Some respirators require medical screening and fit testing.

Respiratory Protection Program: An OSHA requirement whereby any employer who requires or permits employees to wear a respirator must have a written Respiratory Protection Program. The written respirator program establishes standard operating procedures concerning the use and maintenance of respiratory equipment. In addition to having such a written program, the employer must also be able to demonstrate that the program is enforced and updated as necessary. 

Retrofit: The modification of an existing building or facility to include new systems or components. 

Roof Slope: The angle of a roof surface measured in the number of inches of vertical rise in a horizontal length of 12 in.

Roofing Foam: Spray polyurethane foam used in exterior roofing applications. Roofing foam nominal core density is typically 40–56 kg/m3 (2.5–3.5 lb/ft3) and compressive strength is typically 280 kPa (40 lb/in.2) minimum. Building codes do not limit the smoke development index (per ASTM E 84) for roofing foams; therefore, roofing foams should not be used for interior applications.

Rigid Wrap-Around Insulation: Sections of insulation material that have been adhered to a facing to give rigid insulation materials greater flexibility of application.


Saddle:  A relatively small raised substrate or structure constructed to channel or direct surface water to drains or off the roof. A saddle may be located between drains or in a valley, and is often constructed like a small hip roof or like a pyramid with a diamond-shaped base.

Sag: Undesirable excessive flow or run in material after application to a sloped or vertical surface.

Saturation Humidity: The maximum concentration of water vapor in the air at a given temperature before condensation occurs.

Scarf (Scarify): To remove the surface or coating from polyurethane foam by cutting, grinding, or other mechanical means.

Scrim: A woven, non-woven, or knitted fabric, composed of continuous strands of material used for reinforcing or strengthening membranes. Scrim may be incorporated into a membrane by the laminating or coating process. 

SCV: Solid content by volume.

Sealant: Any of a variety of compounds used to fill and seal joints or openings in wood, metal, masonry, and other construction materials. Some common types of sealants are Neoprene, polysulfide, acrylic latex, butyl, polyurethane, foams, and silicone.

Sealant Foam: One- or two-component polyurethane foam typically applied as a bead and used to control air leakage as part of an air barrier system within the building envelope. Sealant foams generally have nominal core densities of 8–40 kg/m3 (0.5–2.5 lb/ft3).

Self-Flashing: The ability of sprayed polyurethane foam to be applied around a penetration or at a roof transition without the need for other materials.

Service Temperature Limits: The maximum continuous temperature at which a coating, polyurethane foam, or other material will perform satisfactorily.

Set: To convert into a fixed or hardened state by chemical or physical action.

Set of Foam: A container of A-side (MDI) and a container of B-side (polyol or resin blend) that can be combined through mixing equipment to form SPF. A set of foam consists of two containers, typically 55-gallon drums.

Shelf Life (Storage Life): The period of time within which a material remains suitable for use.

Silicone: A flexible polymeric elastic substance that is used to seal up gaps, cracks, joints and holes to prevent heat transfer, air leaks and moisture incursion.

Silicone Coating: A liquid-applied, solvent dispersed, elastomeric protective coating whose principal polymer in the dispersion contains more than 95% silicone resin. Some high-solids silicone coatings may have little or no solvent content

Single-Component Foam: A fully formulated foam system packaged in a single aerosol can or pressurized cylinder. Essentially a moisture cure polyurethane prepolymer in a pressurized container. Also called One-Component Foam or OCF. 

Skinning: The formation of a dense film on the surface of a liquid coating or mastic.

Slit Samples: Small cut samples approximately 2 in. long, 1/2 in. wide, and 3/4 in. deep that are taken for evaluation of sprayed materials.

Smooth Surface Texture: The surface texture of SPF that exhibits spray undulation and is ideal for receiving a protective coating. Even though the surface texture is classified as smooth, this surface requires at least 5% additional coating material. 

Soffit Board: A panel, usually made of wood, aluminum, fiber cement or vinyl that covers the bottom of roof eaves where they extend out past the exterior wall. Soffit boards are ventilated to allow air circulation in attic spaces.

Soffit Vents: Holes or slats in soffit boards that let air circulate through the attic space to vent out excess heat and humidity, preventing moisture damage problems such as wood rot and flattened insulation.

Solar Attic Fan: An exhaust fan that operates using solar energy. Attic fans suck up hot air and humidity that rises into an attic space and deposit it outside where it can't cause moisture and heat damage issues.

Solids Content: The percentage of non-volatile matter in a coating or mastic formulation; may be expressed as a volume or weight percent.

Solvent: A liquid that dissolves other substances.

Sound Transmission Class (STC): An integer rating of how well a building partition reduces airborne sound. STC is widely used to rate interior partitions, ceilings/floors, doors, windows, and exterior wall configurations.

SPFA Documents: Technical and informational documents published by the Spray Polyurethane Foam Alliance (SPFA) for use by members and distribution to the public. Documents are numbered “SPFA-XXX.” (Previous documents were designated “AY,” which was developed as part of a numbering system by the Society of the Plastics Industries.)

Spray Foam InsulationFoam or fibrous insulation materials that are applied to a surface with the use of a power spray tool.

Spray Polyurethane Foam (SPF): A foamed plastic material formed by the reaction of an isocyanate and a polyol, and by employing a blowing agent to develop a cellular structure. Spray polyurethane foam may be a two-component reactive system mixed with a spray gun or a single-component system that cures by exposure to moisture. SPF can be formulated to have physical properties appropriate for the application requirements, such as density, compressive strength, closed cell content, and R-Value. Common uses of SPF include insulation, air barriers, and roofing membranes.

Spray Polyurethane Foam (SPF)—High Pressure: Spray polyurethane foam where the A- and B-components are delivered at a pressure between 1000 and 1300 psi, at a rate up to 30 lb/min wherein the components are atomized and impingement mixed in a spray gun.

Spray Polyurethane Foam (SPF)—Low Pressure: Spray polyurethane foam where the A- and B- components are delivered a pressure of less than 250 psi, at a rate between 5 and 7 lb/min wherein the components are mixed using a static mixing nozzle. Components are typically delivered in pressurized tanks.

Square: A standard measurement for roofing area equal to 100 square feet. Also called “roofing square.”

Stack Effect: Also referred to as the “chimney effect,” stack effect results from air density differences between building interiors and exteriors. During heating seasons, the stack effect results in higher relative pressures at the tops of buildings and lower relative pressures at the bases of buildings. These pressure differences can drive air infiltration/exfiltration. Proper sealing measures, such as air barriers formed by SPF and sealants, can mitigate stack effect.

Stress: An applied force that tends to deform a body. May be tensile stress (pulling or stretching force), compressive stress (pushing or compacting force), or shear stress (opposite, but offset parallel forces tending to produce a sliding motion).

Stress-Crack: External or internal cracks within a material caused by long-term stress.

Substrate: The surface to which polyurethane foam is applied.

Supplied-Air Respirator (SAR):  Often referred to as an airline respirator. These devices provide air to the user, through an airline, from a source located some distance away.

Surface Erosion: The wearing away of a surface due to abrasion, dissolution, or weathering

Surface Texture: The resulting surface from the final pass of SPF. The following terms are used to describe the types of SPF surfaces: smooth, orange peel, coarse orange peel, verge of popcorn, popcorn, treebark, and overspray.

Surfacing: The top layers of a roof covering, specified or designed to protect the underlying roofing from direct exposure to the weather.

Surfactant: Short for “surface active agent.” Used to alter the surface tension of liquids. An ingredient in polyurethane foam formulations to aid in mixing and controlling cell size.


Tack-Free: A curing phase of polyurethane foam wherein the material is no longer sticky.

Tack-Free Time:  The time between the start of mixing the two SPF-forming components and the time that the surface of the foam can be touched with a wooden stick without it sticking.

Tear Strength: The maximum force required to tear a specimen, the force acting substantially parallel to the major axis of the test specimen. Values reported as a stress per unit of thickness.

Tensile Strength: The tensile (pulling or stretching) force necessary to rupture a material sample divided by the sample’s original cross sectional area. Units are usually kPa or psi or lb/in2.