Spray Foam Glossary | Best Spray Foam

Air barrier Building science

An air barrier limits uncontrolled airflow through the building enclosure. Its continuity at seams, transitions, and penetrations matters as much as the material used.

See how air and vapor control differ Spray Foam Guides

Air sealing Building science

Air sealing closes leaks at joints, penetrations, and transitions to reduce uncontrolled airflow. R-value alone does not describe this function.

Plan a continuous air-control layer Spray Foam Guides

Application temperature Materials and application

Application temperature covers the product, air, and substrate conditions allowed during use. The exact ranges on the label and technical documentation govern expansion, adhesion, cure, and yield.

Check whether today’s conditions fit the job

ASTM E84 Safety and code

Also: E84, ASTM E-84, surface burning characteristics

ASTM E84 is a laboratory test that burns a sample in a tunnel and reports two numbers: a flame spread index for how fast flame travels across the surface, and a smoke developed index for how much smoke it makes. Both are needed. A sheet that prints one of them has told you half the result, and both change with the thickness the sample was tested at, so a figure without a thickness cannot be compared with one that has it. The test describes a surface under laboratory conditions and says nothing about how an assembly behaves in a fire.

How to read an E84 result

Authority having jurisdiction (AHJ) Safety and code

Also: AHJ, code official

The authority having jurisdiction, often shortened to AHJ, interprets and enforces applicable code and permit requirements. A listing claim does not replace its decision.

See how we treat fire and code claims

Board foot Performance and quantity

Also: board feet, bd ft

One board foot is a volume of 12 inches by 12 inches by 1 inch. It estimates material volume, not R-value or guaranteed field coverage.

Calculate board feet and compare coverage

Class A Safety and code

Class A usually describes a result within a specified surface-burning test and tested configuration. It does not by itself permit exposed foam or approve every assembly.

Read fire claims on the correct basis

Closed-cell foam Materials and application

Also: closed-cell spray foam

Closed-cell foam is a denser, more rigid foam category with mostly closed cells. R-value, vapor behavior, approved uses, and required thickness remain exact-product questions.

Compare open-cell and closed-cell products

Cure Materials and application

Also: curing

Cure is the process by which applied foam develops its intended properties. Time, temperature, moisture, mixing, and thickness can affect it, so the exact instructions govern.

Recognize foam that may not have cured correctly Spray Foam Guides

Draftstopping Safety and code

Also: draft stop, draft stopping

Draftstopping is material or construction installed to restrict the movement of air within large concealed spaces such as floor-ceiling assemblies and attics, dividing one big space into smaller ones. Fireblocking closes the concealed paths between spaces; draftstopping subdivides a space; a firestop seals a penetration in a rated assembly. A maker that calls a can a “draft stop” is naming a use, not a test, and the color of the foam establishes none of the three.

See what fire block foam documents

Expansion rate Performance and quantity

Expansion rate describes how much foam grows after dispensing. High expansion can help fill an approved joint or narrow opening but does not automatically mean higher R-value, better control, or suitability for a whole surface.

Choose a sealant by the job it must do

Fireblocking Safety and code

Also: fire block, fire blocking

Fireblocking is material installed to resist the free passage of flame and hot gases to other parts of a building through concealed spaces, at the locations the residential code prescribes: between floors, at soffits and drop ceilings, around chimneys and similar. It is a building requirement, not a product rating. A can sold as “fire block” foam is making a fireblocking claim, and a surface-burning result such as ASTM E84 or UL 723 does not establish it; the evidence would be a fireblocking or room-corner test with a listing or report number. It is not draftstopping, which subdivides a large concealed space, and it is not a firestop, which is a listed system at a penetration in a rated assembly.

See what fire block foam documents

Firestop Safety and code

Also: firestopping, through-penetration firestop

A firestop is a tested system of specific components around a penetration or joint in a fire-resistance-rated wall or floor, evaluated as an assembly under methods such as ASTM E814 or UL 1479 and identified by a listing. It is not fireblocking, which is a wood-frame requirement for concealed spaces, and not draftstopping. No foam sealant on this site is listed as a firestop system, several makers say so on their own sheets, and “penetration sealant” or “fire rated” wording on a can does not create a listing.

Understand why firestop is a system

Foam sealant Materials and application

A foam sealant fills or seals joints, cracks, and penetrations. It should not be treated as a whole-wall insulation kit merely because it expands.

Choose a foam sealant by application

Gap filler Materials and application

Also: gaps and cracks foam

A gap filler is expanding foam dispensed as a bead into cracks, joints, and narrow openings. Expansion is not proof of surface insulation performance.

See why insulation foam is not gap filler

Ignition barrier Safety and code

An ignition barrier is a code-defined protective layer used in certain limited-access spaces and conditions. It is not interchangeable with a thermal barrier for occupied areas.

Compare ignition and thermal barriers

Isocyanates Safety and code

Isocyanates are reactive chemicals used to make polyurethane products, including spray foam. Spraying can create inhalation, skin, and eye exposure that requires product-specific controls.

Understand the chemical-exposure boundary Spray Foam Guides

Lift Materials and application

Also: foam lift

A lift is a layer or pass of foam applied to a specified thickness. Maximum thickness and time between lifts are exact-product limits that affect heat, cure, and quality.

See how application process changes by system Spray Foam Guides

Off-ratio foam Materials and application

Also: off ratio

Off-ratio foam results when a two-component system does not deliver its chemicals in the intended proportion. Soft, sticky, brittle, discolored, or persistently odorous material is a stop signal.

Respond safely to soft or sticky foam Spray Foam Guides

One-component foam Materials and application

Also: 1K foam, single-component foam

One-component foam is supplied ready to dispense and typically cures using moisture in the air or substrate. Gap sealants and open-surface products can share this chemistry but are not interchangeable.

Compare one-component and two-component formats

Open-cell foam Materials and application

Also: open-cell spray foam

Open-cell foam is a lower-density, softer foam category with interconnected cells. Its thermal, air-control, vapor, and water behavior must be confirmed for the exact product and assembly.

Compare open-cell and closed-cell products

Overspray Materials and application

Overspray is material that lands outside the intended application area. It reduces usable coverage and can damage nearby finishes, vehicles, equipment, or property if containment is poor.

Plan containment and safety before spraying

Personal protective equipment (PPE) Safety and code

Also: PPE

Personal protective equipment, or PPE, can include respiratory, eye, face, skin, and body protection selected for the exact task. It supplements isolation and ventilation.

Place PPE within a complete exposure-control plan Spray Foam Guides

R-value Performance and quantity

Also: thermal resistance

R-value measures resistance to heat flow under stated test conditions. Product claims must be compared at the same thickness, and the number does not describe whole-assembly performance by itself.

See how we compare spray foam R-value claims

Re-entry Safety and code

Also: re-entry period

Re-entry means returning to a work area under specified conditions and may refer to trained, protected workers. It is not automatically the same as occupant re-occupancy.

Plan ventilation and product-specific re-entry Spray Foam Guides

Re-occupancy Safety and code

Re-occupancy is the point when residents, children, pets, or other unprotected occupants may use the space again. It can require a different threshold from worker re-entry.

Separate re-entry from re-occupancy Spray Foam Guides

Safety Data Sheet (SDS) Safety and code

Also: SDS

A Safety Data Sheet, or SDS, describes product hazards, handling, protective measures, and emergency information. Use the document for the exact product and formulation.

Use the SDS within an exposure-control plan Spray Foam Guides

Spray polyurethane foam (SPF) Materials and application

Also: SPF, spray foam

Spray polyurethane foam, or SPF, is a broad family of polyurethane products created or applied as a spray. Small sealants, portable kits, and professional systems differ in controls and approved use.

Learn what spray foam insulation includes Spray Foam Guides

Substrate Materials and application

The substrate is the surface receiving the foam, such as wood, masonry, metal, or a membrane. Cleanliness, dryness, temperature, compatibility, and condition affect adhesion and cure.

Check substrate and application conditions Spray Foam Guides

Surface-spray insulation kit Materials and application

Surface-spray insulation kit is our category for gun-applied products positioned to cover open walls, ceilings, or similar surfaces at controlled thickness. It is an editorial category, not a universal industry certification.

Compare the current surface-spray research set

Thermal barrier Safety and code

A thermal barrier is a protective material or system intended to delay temperature rise of foam under specified conditions. Acceptance depends on the foam, location, evaluation, and applicable code.

Compare thermal and ignition barriers

Thermal bridging Building science

Also: thermal bridge

Thermal bridging occurs where framing, fasteners, or other conductive paths bypass or weaken insulation. It is one reason cavity R-value is not the same as whole-wall performance.

See how thermal bridges change performance Spray Foam Guides

Thermal conductivity Performance and quantity

Also: lambda, lambda value, k-value

Thermal conductivity, written as lambda and given in W/mK, is what European and German data sheets publish instead of an R-value. It runs the opposite way from R: lower conducts less and insulates better. Dividing 0.1442 by the W/mK figure gives an imperial R-value per inch, which is arithmetic rather than a result from any of the ASTM tests the FTC rule names.

See how to read a metric data sheet

Two-component foam Materials and application

Also: 2K foam, A/B foam

Two-component foam mixes two reactive chemicals during application. Ratio, component temperature, flow, nozzle condition, ventilation, and worker protection affect safety and result quality.

Compare portable two-component systems

U-factor Performance and quantity

Also: U-value, thermal transmittance

U-factor is the rate of heat flow through an assembly, equal to 1 divided by R-value, so a lower U is better where a higher R is better. Codes, window labels and whole-assembly calculations use it because U values can be area-weighted and added across paths of differing resistance, which R-values cannot.

See how U-factor and assembly R-value are worked out

UL 723 Safety and code

Also: UL723, ANSI/UL 723

UL 723 is the same surface-burning test as ASTM E84, published by UL rather than ASTM, and it reports the same two indices. Seeing both named on one sheet is normal and does not mean the product was tested twice. What matters is unchanged: both indices, and the thickness they were measured at.

How to read an E84 result

Vapor retarder Building science

A vapor retarder limits water-vapor diffusion according to measured permeance. It is not the same as an air barrier, and its suitable class and location depend on climate and assembly.

Separate vapor control from air control Spray Foam Guides

Whole-wall R-value Building science

Also: assembly R-value, effective R-value

Whole-wall R-value rates the entire opaque wall, including studs, plates, headers and the joins to roof, floor, windows and corners. It sits below the two figures marketing more often quotes: clear wall, which covers insulation with its framing but no interfaces, and center-of-cavity, which is measured where insulation is deepest and assumes framing is none of the wall. In ORNL testing a 2x6 wall at 24 in on center with R-19 batts rates R-13.7 whole wall against R-16.4 clear wall.

See the measured gap between a label and a wall

Wide-spray foam Materials and application

Also: wide spray can

Wide-spray foam uses a fan-shaped or adjustable pattern to cover a small open surface more broadly than a bead. It should be compared with similar cans, not assumed equal to a full insulation kit.

Compare wide-spray products

Yield Performance and quantity

Yield is the amount of foam a package produces, often stated in board feet under specified conditions. Advertised theoretical yield can exceed usable field yield after temperature, technique, stops, and waste.

Separate advertised coverage from usable yield