Expanding Foams

How to choose the right expanding foam

Foam selection depends on the gap size, whether the joint requires fire performance requirements, and how the foam will be applied.

General gap filling and insulation. A standard one-component expanding polyurethane foam handles most window, door, and general construction gaps, expanding to fill irregular cavities and providing thermal and acoustic insulation once cured.

Fire-separating construction. A fire rated expanding foam is required anywhere the gap sits within a fire-rated wall or floor assembly, tested for fire retardance and smoke sealing rather than general insulation performance alone.

Isocyanate-sensitive environments. An isocyanate-free foam formulation is available for users who need to avoid isocyanate exposure, without giving up expansion and insulation performance.

Small or precision jobs. A low-expansion, precision-nozzle foam suits small penetrations and tight spaces where standard foam would over-expand or waste product.

Reusable, multi-job use. A smart-applicator foam format can be resealed and reused across multiple jobs over several weeks, useful for trades who don’t use a full can in one sitting.

Technical differentiators

• Expansion behaviour: Standard foam expands significantly to fill irregular gaps; low-expansion formats are suited to tight or precision spaces
• Fire performance: Standard foam has no fire rating
• Load capacity: Standard and fire rated foams are non-structural; high-density spray foam provides compressive strength
• Chemistry: Standard polyurethane foam versus isocyanate-free formulations for sensitive environments
• Format: Aerosol for small jobs, bulk two-component spray systems for large-scale insulation and sealing work
• Reusability: Applicator formats can be sealed and reused for several weeks; standard aerosol cans are single-use once opened

Expanding foam application guidance

Dampen the substrate lightly before application, since polyurethane foam cures using ambient moisture and a slightly damp surface improves cure and adhesion. Fill gaps no more than half to two-thirds full, depending on expanding foam type. PU construction foams expand significantly as they cure and overfilling may cause bowing or the need to trim excess waste. Use a foam gun for greater control and less waste on larger jobs, and clean the gun or nozzle after every can with a dedicated foam cleaner to prevent the valve from clogging with cured foam. The important part here is to turn off fully’ the variable flow rate control knob at the back of the gun when it is not in use. Allow the stated cure time before trimming, painting, or loading the foam, and check the product’s fire test report before use in any fire-rated assembly, since substituting an untested foam will void the fire rating. For window and door installation specifically, see our window installation guide, and for structural movement joints in the building envelope, see building envelope expansion joints.

Not sure which expanding foam suits the job? Use our product selector tool, download the product catalogue, contact us directly, or find your nearest stockist.