Expanding foam filler: straw, gun, or the wrong product
Updated: 23 October 2026
A search for expanding foam filler turns up straw aerosols near £6 and gun-grade boxes. None of the twelve amazon.co.uk listings in the [expanding foam comparison](/hub/fillers-adhesives-and-sprays/expanding-foam) is a low-expansion window foam, and none is a tested fire stop. Decide the applicator first, then how many cans, then the job the foam is not allowed to do. Prices are the shelf figures from 19 October 2026. We compared those listings and the review notes, not a lab test. A qualifying purchase on amazon.co.uk can earn us a commission at no extra cost to you.
A search for expanding foam filler turns up straw aerosols near £6 and gun-grade boxes.
A search for expanding foam filler turns up straw aerosols near £6 and gun-grade boxes. None of the twelve amazon.co.uk listings in the expanding foam comparison is a low-expansion window foam, and none is a tested fire stop. Decide the applicator first, then how many cans, then the job the foam is not allowed to do. Prices are the shelf figures from 19 October 2026. We compared those listings and the review notes, not a lab test. A qualifying purchase on amazon.co.uk can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Applicator | Volume | Water line | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Soudal Soudal Soudafoam Gap Filler 750 ml | Gun grade | 1 × 750 ml | Water resistant | 8.7 | about £7.19 | View offer |
 Gorilla Filler Gorilla Filler stone, 2 × 500 ml | Straw | 2 × 500 ml | Weatherproof | 8.3 | about £10.82 | View offer | |
 Gorilla Filler Gorilla Filler 500 ml | Straw | 1 × 500 ml | Waterproof | 9.2 | about £6.75 | View offer |
On this page
Straw, gun, or neither
A straw can is the default when you will finish one gap today and throw the rest away. Penosil’s UK guide puts straw foam at about half the joint, because it keeps expanding after it leaves the tube. Gun foam is filled nearer 60 to 70 per cent, and you can pause if you clean the gun. Soudal’s Gun Gap Filler page says about 65 per cent, and +5 °C to +30 °C. Reviews on the Gorilla Filler 500 ml at £6.75 say the nozzle will not fit a separate applicator. The Soudal 750 ml at £7.19 is gun grade and lists included components as n.a., so without a gun and a cleaner it stays a closed tin. The extra kit is on the gun foam vs straw foam page. A cheaper can in a box of twelve is cheaper only if you will use the box.
What this set actually contains
Gorilla Filler from 151 Products is the white 500 ml straw can, model GF2, 4.3 from 7,701 reviews, listed as waterproof and paintable once cured. The stone twin at £10.82 prints the brand attribute as JKG Unknown. Ferris cream cans at £11.99 and £15.99 share one review block. Gorilla Heavy Duty is a grey 353 ml can at £9.93 with a stated gap of 2.5 cm. Soudal here is Gap Filler, not Window & Door foam. The champagne twin, £12.99 for 2 × 750 ml, prints a full cure of 24 hours and Not Water Resistant. Paint Factory Bond & Fill is the £5.82 straw can, 4.2 from 338. Reviewers describe a hole in the straw and a valve that emptied into the tube.
Price bands on amazon.co.uk
Paint Factory is £5.82, Gorilla Filler is £6.75, and the Soudal gun-grade 750 ml is £7.19 without a gun. For one dry gap, the £6.75 straw can is the one with the large review file. The six-pack is £28.99, about £4.83 a can. The twelve-can boxes are £47.99 and £52.44. A bullet says 3.1 litres per can, while Soudal publishes about 28 litres of free foam for Gun Gap Filler. Free foam is open-air output, not the volume of your joint.
When foam is the wrong product
A uPVC or timber frame is the first exclusion. Standard gap filler keeps expanding, and Penosil says straw foam should not go on joints that might warp. Every Soudal can here is Gap Filler, not Window & Door. A surface field that says window is not a low-expansion test. The frame limit is on expanding foam around windows. Ordinary polyurethane foam is not a tested fire stop. If a service penetration must hold a fire rating, this table is the wrong product. UK REACH restriction 2020/1149, in force for this point from 24 August 2023, expects training before professional and industrial users handle diisocyanates. If the can is paid work, read the Health and Safety Executive page on isocyanates. Wash foam off skin, and do not use solvents.
Common questions
Should I buy straw foam or gun-grade foam?
Buy a straw can when you will finish one gap today. The tube blocks once you start, and reviews on Gorilla Filler and on Gorilla Heavy Duty describe that as one use. Buy gun-grade foam when you already own a gun and a cleaner, or you are willing to add both. The £7.19 Soudal can does not include either.
How big a pack do I need for one hole?
One 500 ml straw can is the household size in this set. A 353 ml tin is smaller still, which matters because you cannot save the rest. A six-pack or a twelve-pack is for someone who foams often. Dividing £47.99 by twelve only helps if those twelve cans get used.
Is Gorilla Filler the same as Gorilla Heavy Duty?
No. Gorilla Filler here is the 151 Products 500 ml can, or the Ferris cream cans that use the same name. Gorilla Heavy Duty is model 115953, 353 ml, grey, with a 2.5 cm gap claim and a 45-minute trim time. The prices and the review files are different.
Can I use this gap filler on a uPVC window?
Not as the frame foam. These cans are high-expansion gap filler. A listing that mentions windows does not add a low-expansion formula. Use a foam the maker labels for windows and doors, and keep the drainage paths open.
Is this foam fire rated?
Nothing in these twelve titles is sold as a tested fire stop. Ordinary polyurethane gap filler is the wrong product for a penetration that has to hold a fire rating. That is a specification question, not a thicker bead of the same can.
Why do some bullets say 3.1 litres when the maker says about 28 litres?
The 3.1 litre line is an amazon.co.uk bullet on two Soudal gun packs. Soudal’s Gun Gap Filler page talks about free foam of about 28 litres. Free foam is uncured output in open air. It is not the volume of foam you should leave in a joint, and the two figures should not be added together or treated as a test of this listing.
Related pages
Sources
Public UK sources used for this comparison. amazon.co.uk prices, stars and review counts were taken from the listings on 19 October 2026.
- HSE isocyanates (retrieved 19 October 2026)
- Retained Regulation (EU) 2020/1149 (retrieved 19 October 2026)
- HSENI diisocyanates (retrieved 19 October 2026)
- Fire safety: Approved Document B (retrieved 19 October 2026)
- Hertfordshire Building Control PU-foam note (retrieved 19 October 2026)
- Soudal Soudafoam Gun Gap Filler (retrieved 19 October 2026)
- Soudal Soudafoam range (retrieved 19 October 2026)
- Penosil UK straw foams and gun foams (retrieved 19 October 2026)
- Polycell Expanding Foam (retrieved 19 October 2026)