The physics in one paragraph
Every warm surface radiates heat towards cooler surfaces across an air gap. How much depends on the surface's emissivity: a plasterboard ceiling radiates freely; polished aluminium hardly at all. Put a low-emissivity foil face on one side of a gap and the radiant transfer across it drops by most of its value. That reduction is expressed as an added thermal resistance for the air space — which is why manufacturers quote performance “including air gaps” and why a foil pressed flat against a board has almost none.
Radiant barrier vs multifoil
| Radiant barrier / bubble foil | Multifoil quilt | |
|---|---|---|
| Construction | One or two foil faces on bubble or thin foam | 10–20 alternating films and wadding |
| Insulation value | Low; mainly the air-gap effect | High; certified thermal resistance |
| Typical use | Sheds, vans, behind radiators, summer heat | Roofs, loft rooms, walls, floors |
| Meets roof U-value alone? | No | Often, in a certified build-up |
Where reflective products earn their keep
- Reducing summer overheating in loft rooms and conservatory roofs.
- Lining outbuildings quickly.
- As the outer faces of a multifoil, providing vapour control and radiant performance in one layer.
We will tell you whether a reflective product is part of the answer or a distraction.
Dust, dirt and emissivity
A dusty foil is a less reflective foil. Products installed with the reflective face upward in an open loft lose performance over time as dust settles. Rafter-level installation with the faces vertical or sloping avoids most of this, which is another reason multifoil belongs on the slope rather than the floor.
Questions homeowners ask
Is reflective insulation the same as foil insulation?
Does reflective insulation work in winter?
- SuperFOIL — product range — checked 2 September 2026
- Energy Saving Trust — Roof and loft insulation — checked 2 September 2026