Spray Foam and Building-Envelope Glossary

Air barrierBuilding 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

Air sealingBuilding science

Air sealing closes leaks at joints, penetrations, and transitions to reduce uncontrolled airflow. It should form a continuous air-control path rather than a collection of isolated foam spots.

Plan a continuous air-control layer

Authority having jurisdiction (AHJ)Safety and code

Also: AHJ, code official

The authority having jurisdiction, often shortened to AHJ, is the local organization or official responsible for interpreting and enforcing applicable code and permit requirements. Product literature does not replace its decision.

Understand where local approval fits

Board footPerformance and quantity

Also: board feet, bd ft

One board foot is a volume of 12 inches by 12 inches by 1 inch. Board feet estimate material volume, not thermal performance or guaranteed field coverage.

Connect board feet, thickness, and yield

Bulk waterBuilding science

Also: liquid water

Bulk water is liquid water from rain, plumbing leaks, or groundwater. Insulation is not a substitute for drainage, flashing, leak repair, or capillary control.

Trace moisture sources and drying paths

Class ASafety 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 satisfy every fire-protection requirement.

Separate common fire and code terms

Closed-cell foamMaterials and application

Also: closed-cell spray foam

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

Compare open-cell and closed-cell by assembly

CureMaterials and application

Also: curing

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

Recognize foam that may not have cured correctly

Dew pointBuilding science

Dew point is the temperature at which air with a given moisture content reaches saturation and condensation can begin on a surface. Insulation and air sealing change surface temperatures and moisture paths.

Understand condensation and moisture movement

Drying potentialBuilding science

Drying potential is an assembly’s ability to release incidental moisture toward the interior, exterior, or both. Low-permeance layers on multiple sides can reduce that ability.

Plan where an assembly can dry

Evaluation reportSafety and code

Also: code evaluation report

An evaluation report documents how an exact product was evaluated against stated code provisions and conditions of use. Verify the formulation, thickness, substrate, covering, and report status rather than relying on a logo alone.

Build a product and fire-documentation packet

FireblockingSafety and code

Fireblocking limits concealed draft openings in locations prescribed by code. “Fire block” foam is not automatically a rated firestop or permission to use the product in every assembly.

Compare fireblocking with firestop systems

FirestopSafety and code

Also: firestopping

A firestop is a tested system of components installed around a penetration or joint in a rated wall or floor assembly. Product color or generic “fire rated” language does not establish a listed system.

See why rated penetrations require systems

Ignition barrierSafety 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

IsocyanatesSafety and code

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

Understand isocyanate exposure boundaries

LiftMaterials and application

Also: foam lift

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

See how application process changes by system

Off-ratio foamMaterials and application

Also: off ratio

Off-ratio foam results when a two-component system does not deliver its components in the intended proportion. Unexpected softness, persistent tackiness or oiliness, unusual brittleness, discoloration, or persistent odor need qualified evaluation; appearance cannot establish mix ratio.

Respond safely to soft or sticky foam

One-component foamMaterials and application

Also: 1K foam

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

Compare one-component and two-component systems

Open-cell foamMaterials 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 by assembly

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; it does not make an uncontrolled work zone safe.

Place PPE within a complete exposure-control plan

R-valuePerformance and quantity

Also: thermal resistance

R-value measures resistance to heat flow under stated test conditions. It changes with thickness and does not by itself describe whole-assembly performance, air leakage, moisture durability, or code compliance.

Understand R-value, thickness, and board feet

Re-entrySafety and code

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 unprotected occupant re-occupancy.

Plan ventilation and product-specific re-entry

Re-occupancySafety and code

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

Keep re-entry and re-occupancy separate

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 sheet for the exact product and formulation, not a generic document from the same brand.

Use the SDS within an exposure-control plan

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 chemistry, scale, controls, and approved use.

Learn what spray foam insulation includes

SubstrateMaterials and application

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

Check substrate and application conditions

Thermal barrierSafety and code

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

Compare thermal and ignition barriers

Thermal bridgingBuilding science

Also: thermal bridge

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

See how thermal bridges change the calculation

Two-component foamMaterials and application

Also: 2K foam, A/B foam

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

Compare one-component and two-component systems

Vapor permeanceBuilding science

Also: permeance, perm rating

Vapor permeance measures how readily water vapor passes through a material or assembly under stated conditions. For spray foam it can change with exact formulation and installed thickness.

Connect permeance with vapor-control strategy

Vapor retarderBuilding science

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

Separate vapor control from air control

YieldPerformance 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, starts and stops, and waste are considered.

Plan with theoretical and usable yield separated