Expanding foam around windows
Updated: 23 October 2026
A draught at the edge of a uPVC window feels like a foam job, and a frame is not a brick hole. Expanding foam around windows keeps growing after it leaves the nozzle. You should know when a short bead on an already fixed frame is plausible, and when the can in this comparison is the wrong product. The seven listings, with prices from 19 October 2026, sit on the [insulating spray comparison](/hub/diy-supplies/insulating-spray). A purchase through our links can earn a commission at no extra cost to you.
A draught at the edge of a uPVC window feels like a foam job, and a frame is not a brick hole. Expanding foam around windows keeps growing after it leaves the nozzle.
A draught at the edge of a uPVC window feels like a foam job, and a frame is not a brick hole. Expanding foam around windows keeps growing after it leaves the nozzle. You should know when a short bead on an already fixed frame is plausible, and when the can in this comparison is the wrong product. The seven listings, with prices from 19 October 2026, sit on the insulating spray comparison. A purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Applicator | Volume | Fire class | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Soudal Soudal Soudafoam Gap Filler | Gun grade | 750 ml | n/a | 9.2 | about £7.19 | View offer |
| Best value |  Gorilla Filler Gorilla Filler 500 ml | Straw | 500 ml | n/a | 8.6 | about £6.75 | View offer |
| Alternative |  Bond-It Bond-It Fill 'n' Fix | Gun grade | 750 ml | DIN 4102 Class B3 | 8.2 | about £9.31 | View offer |
On this page
What goes wrong around a frame
Post-expansion is the growth after the bead is already in the joint. Tytan's note says that secondary rise can warp windows and doors if a high-pressure foam is used where a low-pressure window foam was specified. Adkwik lists jammed sashes, warped frames, and cured foam that has to be cut out. A gun improves control. It does not remove post-expansion.
The safe picture is a frame that is already square, screwed, and packed, with a small residual gap. Foam is not a fixing. If the section bows, trimming the face later will not spring it back.
What these seven cans actually claim
None of the seven cans is sold here as a tested low-pressure window foam. Bond-It's Fill 'n' Fix, about £9.31 for 750 ml gun grade, mentions fitting doors and windows and says the foam can reduce the need for mechanical fixings. Do not follow that on a new frame. The same listing states DIN 4102 Class B3 and no fire-resistant additives.
Gorilla Heavy Duty, about £9.93 for 353 ml, names windows and states gaps up to 2.5 cm, and Den Braven's frame sheet gives 2.5 cm as a width not to exceed. Soudal at about £7.19 is a general gap filler. One UK reviewer preferred Soudal's window version for frames.
Order of work if you still use a can
If the frame is already sound, the order is mechanical first. Den Braven's note puts packers about every 50 cm and tells you to leave the supports until the foam has cured, often 24 hours, because cutting too early can restart expansion. Screws stay in. Foam goes into the residual gap in a short bead. The moisture, shake, and fill-short sequence is on the how to use expanding foam page. Around a frame, stay at the low end of whatever fraction your can allows.
Mask the frame and the sill. Solvent cleaner can mark uPVC. Outside, cover the cured bead. Gorilla Heavy Duty tells you to paint outdoor foam, and Soudal's sheet says cured foam is not UV-resistant. If the sash rubs the next day, do not add more foam.
The jobs that are not this can
Hertfordshire Building Control says polyurethane foam only fire-stops the narrow joint that was tested, often with mineral-fibre backing, to BS EN 1366-3 or BS EN 1366-4. Bond-It's B3 line does not become a fire door seal because the title mentions doors. The buying guide separates B3 filler from that specification.
An existing frame, already fixed and packed, can take a short bead if you accept the bowing risk and you cover the outside. A new window, a structural door, or a fire-rated opening waits for a fitter. None of these seven cans is a certified low-pressure frame foam.
Common questions
Can I foam around a uPVC window with a normal can?
You can fill a small residual gap on a frame that is already screwed and packed, and you should expect the foam to keep expanding. You should not foam a new uPVC window into place with Paint Factory, Gorilla, Ferris, Soudal gap filler, or Bond-It from this set. None of them is a tested low-pressure window foam here. One Soudal reviewer preferred the window-specific foam for frames.
Should the window be screwed and packed before I foam?
Yes. Den Braven's frame note puts packers about every 50 cm and tells you to leave the supports until the foam has cured, often 24 hours. Mechanical fixings stay. Foam fills the gap that remains. Bond-It's line about reducing the need for fixings is a listing claim, and it fights that order. Do not omit screws because a can of B3 foam said you might.
Is gun grade safer for frames than a straw can?
It is easier to control, which lowers the chance of a huge bead, and that matters on a frame. Soudal at about £7.19 is gun grade and still a general gap filler. A reviewer wanted the window version instead. Gun grade does not mean low post-expansion, and it does not mean the foam will not bow a section if you overfill. The gun is also not in the can.
Do I need a low-expansion window foam instead?
Yes, if the frame maker or the installer specified one, or if the window is new. illbruck FM330 is an example of that class, with a BBA certificate for its own system. That certificate does not transfer to the seven cans in this comparison. For a hairline draught on an old, solid, already fixed frame, a short bead of general foam is a different and narrower job, and you still cover it outside.
Is foaming a draught the same as spraying the loft?
No. A draught bead around a sound frame is a gap filler. Spray foam on rafters is the product in the RICS consumer guide, with listed-building and valuation issues, and in Commons Library CBP-10658 on mortgages. Buying a straw can for a window board does not put you into those roof cases. Coating the roof with that straw can is the mistake.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Prices stored 19 October 2026. Updated 22 October 2026.
- HSE: Isocyanates (retrieved October 2026)
- HSE: Isocyanate spraying (retrieved October 2026)
- RICS: Spray foam insulation consumer guide (retrieved October 2026)
- Commons Library CBP-10658 (retrieved October 2026)
- Hertfordshire Building Control: PU foam (retrieved October 2026)
- Soudal UK: Soudafoam Gun Gap Filler TDS (retrieved October 2026)
- Polycell: Expanding foam (retrieved October 2026)
- Soudal UK: Filling gaps and holes (retrieved October 2026)