What multifoil is
A multifoil is a flexible quilt built from ten to twenty alternating layers of reflective film, foam and wadding, edged with a reinforced foil face on both sides. The reflective layers cut radiant heat transfer; the wadding holds still air. The main UK brands are SuperFOIL and SOPREMA SuperQuilt (previously YBS SuperQuilt), with Actis and TLX in the same category. Product names differ, the physics does not.
Where it is the right choice
- Loft conversions and room-in-roof where every centimetre of headroom is money.
- Pitched roofs being upgraded from inside without stripping the tiles.
- Dormers, sloping ceilings and awkward shapes where cutting rigid boards is slow and leaves gaps.
- Suspended timber floors where joist depth is shallow.
- Garages, workshops and vans as a fast DIY lining.
Where it is not
An open loft floor. If nobody is standing on it, a 270mm layer of mineral wool at a third of the price is the better buy. And a cavity wall — multifoil is never injected or draped in a cavity.
Six questions and we will tell you whether multifoil, PIR or wool is the sensible starting point for your roof.
Performance and certification
Ask any supplier for the third-party certificate. It will describe the tested build-up — typically the quilt with a 25mm air gap on each face, sometimes combined with a PIR board — and the thermal resistance it achieves. For a pitched roof upgrade in England the target is a U-value of 0.18 W/m²K; most certified multifoils reach it in combination with 50mm PIR or a second quilt, and some claim it alone with larger air gaps. Do not accept a “PIR equivalent” figure without the certificate behind it.
Installing it properly
- Counter-batten the rafters to form a 25mm gap on the cold side.
- Roll the quilt across the rafters, foil faces out, and staple.
- Overlap joints by 50–100mm and tape with the manufacturer's foil tape. Tape every staple line if the product requires it.
- Batten again on the warm side to form the second gap, then plasterboard.
- Keep the eaves and ridge ventilation open, or use a breathable membrane and a designed ventilation path.
Where it works well
- Thin: the roof gets a warm build-up in under 100mm total
- Continuous layer with no cut-board gaps
- Vapour control included
- Fast to install; low waste
- Lightweight
Reasons not to choose it
- Higher cost per m² than mineral wool
- Performance relies on the air gaps being kept
- Needs its own tape system; ordinary tape fails
- Not suitable for cavity walls or as a loft-floor-only product
- Some certification claims assume a combined build-up, not the quilt alone
Cost
Material: £15–£30 per m². Installed to a roof slope, including battens, tape and labour: £45–£80 per m². See foil insulation cost.
Compared with the alternatives
Questions homeowners ask
Is multifoil as good as PIR?
Can I fit multifoil myself?
Does multifoil need a vapour barrier?
How long does multifoil last?
- SuperFOIL — product range — checked 2 September 2026
- GOV.UK — Room in roof insulation best practice — checked 2 September 2026
- Energy Saving Trust — Roof and loft insulation — checked 2 September 2026