Short answer
Multifoil works on timber-frame and stud walls as a thin vapour-resistant layer on the warm side of the studs. It is never used in a cavity, and on solid masonry it is at most one layer inside a designed internal wall insulation system.
- Stud walls: yes
- Cavities: never
- Solid walls: only in a designed system
- Damp walls: fix first
Where foil works on walls
- Timber-frame and stud walls: quilt across the studs on the warm side, battened for the gap, plasterboard over.
- Garage and outbuilding conversions: lining a single-skin wall with a stud frame, multifoil and board.
- Dormer cheeks and room-in-roof stud walls: continuity with the roof multifoil.
- Behind radiators: thin reflective foil as a supplement.
Where it does not
- Cavity walls: no foil product is injected or fitted in a cavity. Cavity fill is the route. Cavity guide.
- Solid masonry walls as sole insulation: a certified internal wall insulation system with designed moisture behaviour is needed; multifoil can be one layer inside such a system but not the whole answer. Internal wall guide.
- Damp walls: a vapour-tight layer over damp masonry traps it.
Stud-wall build-up
- External cladding or masonry outer leaf
- Breather membrane
- Stud with wool or PIR between (optional but usual)
- Multifoil across the warm face of the studs, taped: acts as VCL
- 25mm battens forming the still gap and service void
- Plasterboard
Cost
Multifoil to a stud wall, installed: roughly £35–£60 per m² excluding plasterboard. A single-garage conversion lining, all in: £1,200–£3,000. Indicative, compiled and reviewed 3 September 2026.
Is your wall a foil wall?
The check asks what your walls are; the survey confirms construction before anything is specified.
Questions homeowners ask
Can you use foil insulation on walls?
On timber-frame and stud walls, yes. In cavities, no. On solid masonry only within a designed internal wall insulation system.
Does foil insulation work on internal walls?
On the warm side of an external stud wall, yes. On a plastered masonry wall it is not the primary insulation.
Can foil go in a cavity wall?
No.
Sources and when they were last checked
- SuperFOIL — product range — checked 2 September 2026
- GOV.UK — Approved Document L, Volume 1: Dwellings (current edition, as amended) — checked 2 September 2026
- BSI — BS 5250:2021 Management of moisture in buildings — checked 2 September 2026