10 Best Foam Fillers to Seal Leaks on Window and Door Gaps (UK 2025)

When it comes to protecting your home, the gaps around your windows and doors are often the “weakest link.” In the UK, where driving rain and high humidity are constant challenges, these small crevices do more than just let in a breeze—they are primary entry points for penetrating damp and a major cause of condensation.

If these gaps aren’t properly sealed, warm air from your home escapes, hitting the cold external frame and turning into liquid water. Over time, this leads to black mould and rotting timber.

Choosing the right foam filler is the most effective way to solve two problems at once: it provides a physical barrier to seal leaks and offers deep insulation to eliminate the cold spots that cause dampness.

In this guide, we’ve compared and ranked the 10 Best Foam Fillers to Seal Leaks on Window and Door Gaps (UK 2025) to help you keep your home dry, warm, and mould-free.

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Top 10 Best Foam Fillers for Sealing Leaks and Insulating

1. Fischer 569386 B3 Triple X Expanding Hand Foam – 670ml

Finding a gap around your window frame is annoying, but fixing it shouldn’t be a headache. This Fischer Triple X foam is a solid choice if you want to get the job done without buying extra tools. It’s a hand-held can, so you don’t need a fancy applicator gun.

It expands quite a bit, filling those deep crevices where cold air hides. It hardens fast, too. This means you aren’t standing around waiting for ages. It’s a simple, yellow foam that keeps the rot away and helps quiet down the street noise.

Key Features

• Rapid-hardening formula to speed up your project.
• Hand-held nozzle included, so no applicator pistol is required.
• Effective noise-reducing properties for a quieter home.
• High resistance to rotting over long periods.
• Large 670ml capacity suitable for multiple gaps.

Pros

• Excellent value for money compared to trade brands.
• Dries very quickly once applied to the gap.
• No extra equipment costs for the homeowner.
• Strong expansion capacity to fill deep voids.

Cons

• It can be tricky to control without a trigger gun.
• Results can be messy if you aren’t careful with the nozzle.

Why we recommend Fischer B3 Triple X

We love this one for quick DIY fixes. It’s cheap, fills huge gaps effectively, and resists rot, making it a reliable barrier against nasty drafts.

Check prices on Amazon: Fischer 569386 B3 Triple X Expanding Hand Foam 670ml

2. JKG Unknown Original Gorilla Weatherproof Filler – 2 x 500ml Each

If the Fischer Triple X we just looked at is your go-to for quick internal fixes, this JKG Unknown pack is the heavy hitter for your home’s exterior. Unlike the bright yellow finish of the Fischer foam, this one comes in a stone colour. This makes it much easier to hide against your brickwork or window sills. It’s specifically built to live outside.

Being weatherproof means it won’t crumble when the rain starts lashing against your window gaps. You get two cans in this pack, which is great because, as many DIYers know, one can is rarely enough once you start hunting for drafts.

Key Features

• Specifically formulated for outdoor use with weatherproof properties.
• Natural stone colour for a more discreet finish on masonry.
• High-quality expansion that creates a tight, effective seal.
• Fast-drying formula helps you finish your repair work sooner.
• Comes as a two-piece set providing 1000ml of total filler.

Pros

• Excellent at sealing gaps against harsh driving rain.
• Very easy to work with for standard DIY tasks.
• Effective at creating a durable, long-lasting moisture barrier.
• Good quality foam that doesn’t feel flimsy once cured.

Cons

• The application tubes can block up after the first use.
• Expansion isn’t as huge as the Fischer Triple X foam.

Why we recommend JKG Unknown Original Gorilla

We like this for external window seals. Its weatherproof nature and stone colour make it a practical, sturdy option for blocking rain and insulating your frames.

Check prices on Amazon: JKG Unknown Original Gorilla Weatherproof Filler 2 x 500ml Each

3. Haltons Ready To Use Expanding Foam Filler – 500 ml

If you found the JKG Unknown pack a bit too much for a small job, this Haltons filler is a great single-can alternative. It positions itself as a versatile all-rounder, much like the Fischer Triple X, but with a heavy focus on being “ready to use” right out of the box.

It bonds to almost anything—stone, wood, or even metal. This makes it handy if you’re sealing a gap where a window frame meets a brick wall. It dries in about an hour, so you aren’t waiting all day to sand it down or paint over it. It’s a straightforward, no-nonsense tool for those nagging household holes.

Key Features

• Rapid expansion formula designed to fill large voids and cracks quickly.
• A dedicated spray nozzle is included, so no extra tools are needed.
• Multi-surface adhesion works on wood, metal, brick, and ceramic.
• Waterproof and soundproofing properties for internal and external use.
• Quick-dry chemistry allows for sanding or painting within sixty minutes.

Pros

• Extremely easy for beginners to use without any technical setup.
• Very sticky consistency ensures it stays exactly where you spray it.
• Faster drying time than many other budget-friendly foam fillers.
• Versatile enough for both bathroom plumbing and window insulation.

Cons

• Several users have reported issues with the nozzle becoming faulty.
• Stickiness makes it very difficult to clean off skin or clothes.

Why we recommend the Haltons Foam Filler 500 ml

We recommend this for small, varied repairs. It’s a reliable “toolbox staple” that handles different surfaces well, providing a quick waterproof seal for any home.

Check prices on Amazon: Haltons Ready To Use Expanding Foam Filler 500ml

4. Gorilla Filler Weatherproof Expanding Foam Filler – 500ml

Did you find the JKG Unknown twin-pack a bit too much for your needs? This single can is the same “cousin” in a smaller size. It’s the same reliable, waterproof formula, perfect for when you only have one or two windows to tackle. Unlike the Haltons filler, which is more of a general-purpose household tool, this version is a specialist at stopping water.

It creates a completely airtight seal that standard foams—like the Fischer one we started with—sometimes struggle to maintain in wet weather. Just like its JKG twin, it bonds to stone and brick with ease and can be sanded back once dry.

Key Features

• High-performance waterproof and airtight sealing capabilities.
• Specifically recommended for bathroom fixtures and high-moisture areas.
• Versatile adhesion to stone, wood, brick, metal, and plastic.
• Fully sandable and paintable once the curing process finishes.
• High-density expansion that squeezes into the tightest cracks.

Pros

• Creates an incredibly strong barrier against penetrating damp.
• Much better at blocking drafts than standard non-weatherproof foams.
• Very easy to paint over to match your existing window frames.
• Identical professional quality to the JKG Unknown version.

Cons

• The delivery tube is prone to clogging very quickly after use.
• Some users find it difficult to dispense a consistent amount.

Why we recommend Gorilla Filler Expanding Foam Filler – 500 ml

We recommend this for anyone dealing with serious water ingress. It’s a tough, reliable foam that ensures those pesky gaps stay sealed and dry through the winter.

Check prices on Amazon: Gorilla Filler Weatherproof Expanding Foam Filler – 500 ml

5. Fischer 567427 Triple X Hand Foam (H3)

Did you notice how similar this looks to the first Fischer product we discussed? This 567427 version is essentially the same “Triple X” family member, offering that familiar bright yellow seal for those who trust the brand. It’s a straightforward hand-held can that doesn’t force you to buy a separate applicator gun.

While the Gorilla cousins focus on weatherproofing, this Fischer foam is all about speed and noise reduction. It hardens remarkably fast, which is a lifesaver when you’re trying to finish a job before the sun goes down. It’s particularly good at deadening sound, making it a smart choice for gaps near busy roads.

Key Features

• Rapid-hardening formula significantly reduces project downtime.
• The ready-to-use handheld nozzle requires no extra equipment.
• Noticeable noise-reducing properties for quieter interiors.
• Highly resistant to rot and aging once fully cured.
• Excellent adhesion to common building materials, such as masonry.

Pros

• Professional-level results for a very low price point.
• Extremely simple to operate even for total beginners.
• Fills deep holes and gaps with a very high expansion rate.
• Dries quickly enough to be trimmed back the same afternoon.

Cons

• The foam is incredibly sticky and hard to clean off hands.
• Expansion can be unpredictable, sometimes filling more than expected.

Why we recommend Fischer 567427 Triple X

We recommend this for budget-conscious DIYers who need a fast, rot-resistant seal. It’s a reliable brand mate to our top pick that excels at blocking out both drafts and street noise.

Check prices on Amazon: Fischer 567427 Triple X Hand Foam

6. Gorilla Heavy Duty Expanding Foam 353ml

You still remember the other Gorilla Filler options we’ve mentioned? This version is the premium sibling in the family. While the earlier Gorilla cousins focus specifically on being weatherproof out of the can, this brand-mate is a beast at structural sealing. It promises zero shrinkage, which is a massive plus when you’re trying to block out pests or stubborn drafts that standard foams might miss.

It gets tack-free in just about ten minutes, making it much faster to work with than many basic fillers. Just keep in mind that if you use it outside, you’ll need to paint it to protect it from the sun, unlike the stone-coloured weatherproof version.

Key Features

• High-density formula designed to seal gaps and cracks up to 2.5cm.
• Zero shrinkage ensures the seal remains airtight and pest-proof forever.
• Extremely fast curing time, becoming tack-free in 8-12 minutes.
• Multi-material bond works on PVC, plaster, brick, and even skylights.
• Paintable and sandable surface for a completely seamless DIY finish.

Pros

• Superior at blocking out air and moisture in critical areas.
• Much less likely to pull away from the edges than cheaper foams.
• The small 353ml can size is perfect for precision work in tight spots.
• Versatile enough for both attic vents and plumbing gaps.

Cons

• Requires painting for outdoor use to prevent UV discolouration.
• Some users found that the nozzle can stop working before the can is empty.

Why we recommend Gorilla Heavy Duty Expanding Foam 353ml

We recommend this if you need a “set and forget” seal that won’t shrink over time. It’s a high-quality family member of the Gorilla range that offers maximum protection against both weather and pests.

Check prices on Amazon: Gorilla Heavy Duty Expanding Foam 353ml

7. Professional soma fix Expanding Foam

Are you looking for something that can handle even tougher conditions than the standard fillers we’ve seen? While the Fischer Triple X is great for quick internal fixes, this professional soma fix is a true survivor. It goes a step beyond being “all-weather” by being resistant to seawater, dilute acids, and even steam.

This makes it a unique alternative to the Gorilla range if you are working in particularly harsh environments—like a coastal home or a high-moisture utility room. It cures relatively quickly, fully hardening in as little as one to three hours, which keeps your project moving at a professional pace.

Key Features

• Chemically resistant formula that stands up to seawater, acids, and steam.
• High-strength polyurethane bond for concrete, wood, metal, and plastic.
• All-weather performance suitable for year-round indoor and outdoor use.
• Fast-acting cure that allows for trimming and painting within 1–3 hours.
• Straw nozzle application designed for filling deep pipe penetrations and wall gaps.

Pros

• Exceptional durability in environments where standard foams might degrade.
• Highly effective at blocking out not just drafts, but also dust and noise.
• Very stable volume that provides long-lasting structural stability.
• Versatile enough to be used on everything from boat repairs to window frames.

Cons

• Higher price point per litre compared to the Fischer and Haltons options.
• Requires careful handling due to its professional-strength chemical makeup.

Why we recommend professional soma fix

We recommend this for specialised jobs where environmental resistance is the priority. If you need a seal that won’t flinch at steam or salt air, this is the most robust choice in our lineup so far.

Check prices on Amazon: Professional Soma Fix Expanding Foam

8. Soudal 130585 Soudafoam Gap Filler (H3)

Did the Fischer Triple X catch your eye for its professional results, but you want even more precision? This Soudal 130585 is the “Gun Grade” counterpart to the hand-held foams we’ve looked at. Unlike the professional soma fix or the Gorilla cans that use a simple straw, this one is designed to be used with a foam applicator gun.

This means you get much finer control over the bead size, which is a massive help if you’re filling narrow window gaps where too much expansion could cause a mess. It uses Soudal’s “DuraValve” technology, which helps the can stay usable for longer, even if you don’t use it all in one go.

Key Features

• Gun-grade design for pinpoint accuracy and reduced product waste.
• High 3D expansion that fills deep voids without leaving internal air pockets.
• Excellent acoustic rating (up to 58 dB) for superior soundproofing.
• Heat and water-resistant formula that stands up to ageing and rot.
• Large 750ml canister provides a much higher yield than the smaller Gorilla cans.

Pros

• Offers the most controlled application of any foam on our list so far.
• Incredible sound insulation, making it the best choice for street-facing windows.
• Adheres brilliantly to almost all building materials (except PE/PP).
• Very stable once cured, with no significant shrinkage or post-expansion.

Cons

• Requires a separate foam applicator gun and cleaner to use.
• Not UV resistant, so it must be painted or covered if used outdoors.

Why we recommend Soudal 130585 Soudafoam Gap Filler-750ml

We recommend this for anyone who already owns a foam gun or has a large project ahead. It’s a high-yield, professional-grade alternative to the Fischer range that gives you the cleanest finish possible when soundproofing or insulating door frames.

Check prices on Amazon: Soudal 130585 Soudafoam Gap Filler-750ml

9. Professional Soma Fix Dual Nozzle Expanding Foam 750ml

Did you notice the “dual” advantage here? This is the high-performance sibling to the professional soma fix we just saw, but it adds a clever twist: a dual-nozzle system in a large 750ml can. It offers the same extreme resistance to seawater and steam, but gives you the choice between a quick-fix straw or a professional gun attachment.

If you’re working on a vertical surface—like a stone wall or a high door frame—this is your best bet because it “grabs” in just 60 seconds. While the Soudal Soudafoam requires you to commit to a gun, this 750ml powerhouse lets you swap styles depending on how tight the gap is.

Key Features

• Dual-nozzle design compatible with both straw and professional foam guns.
• Ultra-fast tack time that grips and “grabs” surfaces in only 60 seconds.
• Massive 750ml capacity expanding to cover up to 45 meters of joint.
• Industrial-grade resistance to moisture, saltwater, and dilute acids.
• High-strength bond specifically designed for concrete, brick, and stone.

Pros

• Perfect for vertical or overhead jobs where you need the foam to stay put fast.
• Provides the flexibility of a professional tool and a DIY straw in one can.
• The 750ml volume makes it very cost-effective for larger renovation projects.
• Does not require external support or bracing during the curing process.

Cons

• The 60-second grab means you have very little time to adjust mistakes.
• Premium price reflects the specialised “instant-grip” chemistry.

Why we recommend the professional soma fix Dual Nozzle 750ml

We recommend this for complex or vertical projects where speed and volume are critical. It combines the chemical toughness of the Soma Fix brand with a versatile delivery system that handles everything from brickwork to blockwork with ease.

Check prices on Amazon: professional soma fix Dual Nozzle Expanding Foam 750ml

10. FERRIS | The Original Gorilla Filler [2 x 500ml]

Did you notice this familiar name? This FERRIS twin-pack is yet another “cousin” to the JKG Unknown and the single-can Gorilla Filler we discussed earlier. It is the same “Original Gorilla” formula, packaged under the FERRIS brand. While the professional Soma Fix 750ml is your go-to for industrial-strength chemical resistance, this FERRIS pack is the classic home-repair champion.

It specialises in that airtight, weatherproof seal that Gorilla is famous for. Getting two 500ml cans is a smart move; it gives you a total of 1000ml of filler, ensuring you don’t run out halfway through sealing a large window frame or a series of brickwork gaps.

Key Features

• The “Original Gorilla” formula is designed specifically for stone, wood, brick, and metal.
• Forms a 100% airtight and weatherproof seal to block out driving rain and drafts.
• High expansion capability that conforms to irregularly shaped cavities easily.
• Fully versatile surface—can be cut, sawn, sanded, and painted once cured.
• Energy-efficient barrier helps maintain indoor temperatures and lower bills.

Pros

• Excellent value for money with two cans providing a large total volume.
• Proven reliability for outdoor gaps that need to withstand the elements.
• Very easy to trim back for a flush, professional finish against masonry.
• Consistent expansion that doesn’t leave hollow pockets inside the wall.

Cons

• Like its cousins, the straw and valve can clog if not cleaned immediately.
• Very sticky formula that requires careful handling to avoid messes.

Why we recommend FERRIS | The Original Gorilla Filler

We recommend this twin-pack for general exterior home maintenance. It’s the same trusted Gorilla quality we’ve seen throughout this list, offering a durable, long-lasting barrier that keeps your home cozy and dry.

Check prices on Amazon: FERRIS | The Original Gorilla Filler (2 x 500ml)

How to Choose The Best Foam Filler in the UK

Choosing the right expanding foam in the UK can feel like a bit of a minefield because “one size” definitely does not fit all. If you use a high-expansion foam in a delicate window frame, you might actually warp the frame; use the wrong one outside, and it’ll crumble within a year.

Here is a simplified guide to help you choose the right “family” of foam for your specific project.

1. Choose Your “Grade”: Hand-Held vs. Gun Grade

This is the first decision you’ll face at the DIY store or on Amazon.

• Hand-Held (Straw Grade): The most common for DIY. It comes with a plastic straw. It’s “one and done”—once you start the can, you usually have to finish it because the straw clogs quickly.
  • Best for: Small, one-off home repairs.
• Gun Grade: Requires a metal applicator gun (sold separately). It offers far more precision and the ability to “dial down” the flow.
  • Best for: Large projects or professionals. You can leave the can on the gun for weeks without it drying out.

2. Match the Foam to the Location

Not all foams handle the British weather the same way.

• Standard PU Foam (Internal): These are great for filling holes behind bath panels or around internal pipes. They are budget-friendly but shouldn’t be left exposed to the sun.
• Weatherproof/Waterproof Foam: As seen with the Gorilla and soma fix ranges, these are designed for external brickwork. They resist driving rain and won’t rot when damp.
• Fire-Rated (Pink) Foam: If you are sealing a gap in a garage wall that connects to your house, or around a fireplace, look for B1 or B2 fire-rated foam. It’s legally required in some building areas to slow the spread of smoke and flames.

3. Consider the “Expansion Rate”

This is where most beginners make a mistake.

• High Expansion: These foams (like Fischer Triple X) grow massively—sometimes up to 40 times their liquid size.
  • Use for: Large cavities, deep holes in masonry, or under floorboards.
• Low Expansion: These are designed to expand just enough to seal a gap without putting pressure on the surroundings.
  • Use for: Plastic window frames and door frames. High expansion foam can actually bend a PVC frame so much that the window won’t close!

The “Golden Rules” for UK DIYers

Mist the Gap: Most foams are “moisture-curing.” Lightly spray the hole with a water mister before you foam. It helps the foam expand fully and stick better.

The 50% Rule: Only fill a gap halfway. It looks like you haven’t used enough, but within 10 minutes, that foam will have grown to fill the entire space.

Don’t Touch it Wet: If you get a “blob” where you don’t want it, do not wipe it. Wiping wet foam just smears it into the surface. Wait 30 minutes until it’s hard, then simply flick it off or slice it with a blade.

Answering Your Common Questions About Foam Filler in the UK