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If you have been researching loft or roof insulation, you will have come across multifoil insulation and foil insulation, plus brands like SuperFOIL. It looks nothing like the fluffy rolls most people picture, and that puts a lot of homeowners off. So what is foil insulation, does it actually work, and is it right for your home? Here is the plain English version.
Multifoil is a thin, multi-layered product made of reflective foil sheets sandwiched with insulating wadding or foam. Instead of relying purely on thickness to slow heat loss, it reflects radiant heat back into your home. Because it is slim, often just 30 to 40mm, it is popular where there simply is not room for thick rolls or boards.
All foil and reflective insulation works on the same principle: shiny foil surfaces reflect radiant heat rather than absorbing it. For that to work, foil insulation needs an air gap on one or both sides, which is why it cannot simply be squashed tight against another surface. Get the air gaps and sealing right and it performs well, get them wrong and it underperforms, which is the single most important thing to understand about foil insulation.
SuperFOIL is one of the best known multifoil brands in the UK, with products designed for lofts, roofs, walls and floors. Like other multifoils, its strength is performance per millimetre rather than raw bulk. Whichever brand you consider, the same rules apply: check the product's tested performance and make sure it is installed with the correct air gaps.
Foil insulation is at its best in the roof. In a loft conversion or warm roof it is fitted between and under the rafters, insulating the sloped ceiling without eating into headroom. For a standard cold loft floor with plenty of space, traditional rolls are usually the simpler and cheaper choice, so foil earns its place mainly where space is tight or you are creating a room in the roof.
Yes, when it is specified and fitted correctly, but be realistic about the claims. On its own, multifoil often will not reach the U-value required for a warm roof, so it is commonly combined with PIR boards or mineral wool to meet building regulations. Treat headline manufacturer figures with care, look at independently tested performance, and remember that a poorly fitted multifoil with no air gap can badly underperform.
There is no single winner, it depends on the job. Mineral wool is the cheapest way to insulate an open loft floor. PIR boards give the highest performance per millimetre for boarded floors and conversions. Multifoil and SuperFOIL sit between the two: slim, reflective and excellent where space and headroom are at a premium, and basic bubble foil is best kept for outbuildings. A good installer will often use them in combination. For a fuller comparison see multifoil vs traditional insulation and mineral wool vs Rockwool vs PIR.
| Factor | Multifoil / SuperFOIL | PIR board (Celotex, Kingspan) |
|---|---|---|
| How it works | Reflects radiant heat, needs an air gap | Resists conducted heat, bulk insulation |
| Thickness | Very slim, often 30 to 40mm, but usually needs air gaps plus another layer | Thin rigid board, high performance per millimetre |
| Quoted performance | System based, test the whole build up, treat "equivalent to Xmm" claims with care | Around 0.022 W/mK, one of the best bulk insulants |
| Meets warm-roof U-value alone? | Often no, usually combined with PIR or mineral wool | Often yes with enough thickness |
| Best for | Tight rafters and sloped ceilings, layered systems | Boarded floors, warm roofs, conversions with room for board depth |
| Install sensitivity | High, needs correct air gaps and sealed joints | Lower, cut and fit tightly, tape the joints |
Worth it in the right place, oversold in the wrong one. Multifoil earns its money where space is genuinely tight: loft conversions, sloped ceilings and between rafters, where a 270mm roll simply will not fit. There, its slim profile buys you insulation without losing headroom. Where you have room for a standard loft roll or PIR board, traditional insulation is usually cheaper for the same result. And on its own, multifoil often will not meet a warm-roof U-value, so budget for it to be paired with PIR or mineral wool. Treat "equivalent to Xmm of mineral wool" marketing with caution and ask your installer for the tested performance of the actual build up. In short: a smart choice for tight spaces and layered systems, not a magic slimline replacement for proper insulation.
Multifoil only performs as promised when it is installed with the right air gaps on either side and properly sealed at the joints. This is exactly why the installer matters as much as the material. It is worth using vetted, accredited insulation installers who know how to detail it correctly. It also helps to understand the recommended loft insulation depth so you can weigh foil against traditional options.
Multifoil insulation is a thin, multi-layered product made of reflective foil sheets sandwiched with insulating wadding or foam. Rather than relying on thickness, it reflects radiant heat back into the home, so it is much slimmer than traditional rolls, often around 30 to 40mm.
Yes, in the right situation. Multifoil is very effective where space is tight, such as between rafters in a loft conversion, and as part of a layered build up. It works differently from bulk insulation rather than simply better or worse, and many homes get the best result by combining multifoil with mineral wool or PIR.
Its performance depends heavily on correct installation with an air gap on one or both sides. On its own it often will not meet the required U-value for a warm roof, so it is frequently combined with PIR boards or mineral wool to hit building regulations targets. Always check the specific product's tested figures and how it is being installed.
Often, yes. For loft conversions and warm roofs, multifoil is commonly paired with rigid PIR boards such as Celotex or Kingspan to reach the required thermal performance in a slim build up. An installer will design the layering around your roof and the standard you need to meet.
Bubble foil is a simpler, thinner product with a bubble-wrap core between foil faces, often used for lower performance jobs like outbuildings. Multifoil has multiple reflective layers and wadding and is designed for higher performance in homes. Multifoil generally outperforms basic bubble foil.
Foil and multifoil insulation is used in lofts and warm roofs between and under the rafters, in walls and behind radiators, and in floors. It suits tight spaces and sloped ceilings especially well. For a flat roof or to meet building regs it is usually combined with other insulation.
If you have headroom to spare, traditional rolls or boards are usually the cheaper route. But for loft conversions, awkward roof spaces and slimline upgrades, multifoil and SuperFOIL insulation can be the ideal solution, provided it is fitted right and, where needed, combined with other insulation to meet building regs. Not sure which suits your home? Tell us about your project and we will advise, then match you with vetted installers so you can compare quotes.
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