Expanding Foam

About Expanding Foam

Expanding foam, also known as polyurethane foam or PU foam, is an essential product for both professional tradespeople and DIY enthusiasts tackling insulation, filling, and fixing projects. This versatile material starts as a liquid dispensed from a pressurised canister or aerosol and rapidly expands to fill gaps, cavities, and voids before curing into a rigid, insulating foam. Our comprehensive range includes hand-held aerosol foams for quick applications and professional gun-grade foams for precision work requiring controlled dispensing.

The expanding foam category features trusted brands including Everbuild, Polycell, Fischer, Ronseal, and Sealey, offering solutions for everything from general gap filling to specialised thermal insulation. Products are available in different expansion rates and formulations – some designed for filling large voids with high-expansion foam, whilst others provide low-expansion precision for fitting door frames and windows. We also stock essential accessories including applicator guns, replacement nozzles, and specialist foam cleaners to maintain your equipment and ensure professional results every time.

Modern expanding foams cure to provide excellent thermal and acoustic insulation properties whilst remaining easy to trim, cut, and finish once set. Most products are ready for overpaining, plastering, or rendering, making them ideal for both structural applications and cosmetic repairs around the home or on site.

Jargon Buster

• Gun-Grade Foam: Professional expanding foam designed for use with a foam applicator gun, offering precise control and allowing the flow to be stopped and started throughout the day without wastage. The canister screws directly onto the gun mechanism.
• Hand-Held or Aerosol Foam: Foam supplied with a single-use straw applicator attached to the canister. Once started, the entire can must typically be used in one session, making it ideal for smaller, one-off jobs.
• Expansion Rate: The degree to which foam increases in volume from its liquid state. Low-expansion foams (around 25-50% expansion) suit precision work like window fitting, whilst high-expansion foams can increase several times in volume for filling large cavities.
• Curing Time: The period required for foam to fully harden and reach its final strength. Surface-dry times typically range from 20-40 minutes, with full curing taking 12-24 hours depending on temperature and humidity.
• Fire-Rated Foam: Specialist expanding foam formulated to provide fire resistance, tested to British and European standards for use around fire doors, service penetrations, and other applications requiring fire protection.
• Dual-Purpose Foam Cleaner: Solvent-based cleaner used both to remove uncured foam from tools and surfaces and to clean foam guns between applications, prolonging equipment life.

Who Uses Expanding Foam?

Expanding foam is an indispensable product across numerous trades and applications:

• Window and Door Fitters: For sealing frames, providing insulation, and ensuring draught-proof installations
• Builders and General Contractors: Gap filling, cavity insulation, and securing pipework or conduits
• Plumbers and Heating Engineers: Sealing pipe penetrations through walls, sound-deadening, and securing boiler flues
• Electricians: Filling holes after cable runs and providing fire-stopping around electrical installations
• Roofers: Sealing roof penetrations, filling gaps in soffits and fascias, and improving loft insulation
• Plasterers and Dry-Liners: Fixing plasterboard to uneven walls and filling voids before finishing
• Shopfitters and Carpenters: Securing architraves, fixing skirting boards to solid walls, and general void filling
• DIY Enthusiasts and Homeowners: Home insulation projects, draught-proofing, and general repairs around the property
• Facilities Managers and Maintenance Teams: Ongoing building maintenance, pest-proofing, and energy efficiency improvements

How to Choose the Right Expanding Foam

Selecting the appropriate expanding foam depends on several key factors:

Application Type: Determine whether you need hand-held aerosol foam for occasional, smaller jobs or gun-grade foam for professional, frequent use. Gun-grade systems offer better value for regular users and allow partial use with minimal wastage.

Expansion Rate: Match the foam to your application – low-expansion foams are essential around window and door frames where excessive pressure could distort frames, whilst high-expansion products efficiently fill large cavities, holes, and gaps in masonry or timber.

Specialised Formulations: Consider whether you require standard general-purpose foam or a specialist product. Fire-rated foams are essential for fire door installations and maintaining compartmentation. Thermal foams offer enhanced insulation properties for energy efficiency projects.

Yield and Coverage: Check the manufacturer's stated yield, typically measured in litres of cured foam per canister. This helps calculate quantities needed for larger projects and ensures cost-effectiveness.

Curing and Trimming Time: Fast-curing foams allow quicker project progression but provide less working time. Standard foams offer a balance between workability and completion time.

Accessories Required: If choosing gun-grade foam, ensure you have a compatible applicator gun. Budget for foam cleaner to maintain your gun between uses, as uncured foam will permanently damage equipment if left to harden.

Popular Accessories

• Foam Applicator Guns: Professional dispensing tools from brands like Sealey that screw onto gun-grade foam canisters, providing precise control and reusability
• Replacement Nozzle Sets: Spare nozzles and extensions offering different spray patterns and reach for various applications
• Foam Cleaners: Specialist solvents for cleaning uncured foam from tools, guns, and surfaces – essential for maintaining professional equipment
• Protective Gloves: Chemical-resistant gloves to protect hands, as uncured foam is difficult to remove from skin
• Safety Glasses: Eye protection when dispensing foam overhead or in confined spaces
• Sharp Trimming Knives: For cutting back cured foam flush with surrounding surfaces before finishing
• PTFE Tape and Sealants: Complementary products for creating complete weatherproof and airtight seals

Safety Information

Expanding foam requires careful handling and appropriate safety precautions:

Personal Protection: Always wear protective gloves when handling expanding foam products, as uncured foam adheres strongly to skin and is extremely difficult to remove. Safety glasses are recommended, particularly when working overhead. Ensure adequate ventilation when using foam in confined spaces, as vapours may cause respiratory irritation.

COSHH Compliance: Tradespeople should be aware that expanding foam products contain isocyanates and other chemicals subject to COSHH regulations. Familiarise yourself with product safety data sheets, particularly for professional or frequent use.

Fire Safety: Use only fire-rated foams where required by Building Regulations, particularly around fire doors, service penetrations in fire-resistant walls, and compartmentation barriers. Standard foam does not provide fire protection.

Storage and Disposal: Store canisters upright in cool, dry conditions away from heat sources and naked flames. Canisters are pressurised and should never be punctured or incinerated. Dispose of empty canisters according to local authority guidelines for aerosols.

Overfilling Risks: Avoid overfilling cavities, particularly around window and door frames, as excessive expansion pressure can cause frames to bow or distort. Use low-expansion foam for such applications.

Frequently Asked Questions

How long does expanding foam take to dry and when can I trim it?

Most expanding foams become tack-free and trimmable within 30-60 minutes, though this varies by product and ambient conditions. Full curing typically takes 12-24 hours. For best results, check the manufacturer's specific guidance on the canister. Warm, humid conditions accelerate curing, whilst cold, dry environments slow the process.

Can I use expanding foam outside and will it deteriorate in sunlight?

Yes, expanding foam can be used externally, but cured foam will degrade when exposed to direct UV light, causing it to discolour and become brittle over time. For external applications, always over-paint, render, or otherwise protect cured foam from sunlight to ensure longevity.

What's the difference between gun-grade and hand-held expanding foam?

Gun-grade foam requires a separate applicator gun that screws onto the canister, offering precise control, the ability to stop and restart application, and minimal wastage between uses. Hand-held foam comes with a disposable straw applicator and must typically be used entirely once started. Gun-grade systems are more economical for professional or frequent users, whilst hand-held cans suit occasional DIY projects.

How do I remove uncured expanding foam from my hands or tools?

Remove uncured foam immediately using a specialist foam cleaner or solvent before it sets. Once cured, foam cannot be dissolved and must be mechanically removed. For skin, use a foam cleaner or wipe with acetone, then wash thoroughly with soap and water. Prevention is better than cure – always wear protective gloves.

Is expanding foam waterproof and suitable for sealing leaks?

Whilst expanding foam is water-resistant once cured and provides excellent gap-filling properties, it's not designed as a primary waterproofing membrane. It works well for filling gaps that may then be sealed with appropriate waterproof coatings, but shouldn't replace proper tanking, damp-proofing, or dedicated water-sealing products for critical applications.