SuperQuilt multifoil insulation in London

What multifoil insulation actually is

SuperQuilt is a multilayer insulation quilt: reflective aluminium foil outer faces with alternating layers of foam and wadding sealed between them. It works on a different principle from mineral wool. Wool slows heat by trapping still air in a thick fibrous matrix — the more depth, the better it performs. Foil works primarily by reflecting radiant heat back the way it came, which is a mechanism that does not depend on thickness at all.

That difference is why the two products are not really competitors, despite constantly being compared. Where you have unlimited depth — a cold loft floor between joists — wool is superb value and hard to beat. Where you have no depth to give — the underside of a rafter in a room that is already low — foil does something wool physically cannot.

Where it makes sense in a London home

The classic case is a room in the roof. A 1930s semi with a converted attic bedroom, or a Victorian terrace whose top floor sits inside the roof slope, will typically have 100mm rafters and a plasterboard ceiling fixed straight to them. To insulate that properly with wool you would need to deepen the rafters by 100mm or more and lose that depth from a room that probably has 2.1 metres of headroom to start with. A 40mm multifoil build-up, battened to preserve the required air gaps, gets you most of the way there while costing you a couple of inches instead of a foot.

The second case is a loft conversion in progress. Builders working to a tight structural envelope routinely specify multifoil precisely because it lets them hit the required U-value without pushing the finished ceiling any lower. We are often called in by the homeowner rather than the builder, to install the insulation layer properly before boarding out begins.

The third is a period roof where the existing structure cannot easily be altered — original timbers, awkward geometry, or a conservation constraint that makes deepening the roof build-up a non-starter.

How we install it

Installation quality matters more with multifoil than with almost any other insulation product, because the product only performs as designed when the air gaps around it are correct. Compressed flat against a surface, it loses most of its benefit and the homeowner never finds out.

1. Survey and specification

   We measure the rafter depth, check the ventilation path behind the roof covering, and calculate the build-up needed to hit the performance you are after. Sometimes the answer is that multifoil is the wrong product for your roof and wool would be cheaper — we say so.

2. Battening out

   Counter-battens create the specified air gap on the cold side, so the foil has an air space to reflect into. This is the step that separates a working installation from an expensive foil-lined room.

3. Fixing and sealing

   The quilt is fixed with the correct overlap at every joint and the seams are sealed with foil tape. Gaps and unsealed laps let convection currents bypass the whole layer.

4. Second batten and hand-over

   An inner batten creates the warm-side air gap and gives your plasterer or boarder a fixing plane. We hand over the declaration of performance for your records.

What it costs

Multifoil is a premium product and the installation is more labour-intensive than rolling out wool, so expect it to sit above mineral wool per square metre. The honest way to think about it is not as a more expensive way to do the same job, but as the only practical way to do a different one. Nobody insulates a cold loft floor with multifoil because it is better value; they use it on a slope because wool would cost them a room's worth of headroom.

Our cost guide covers what drives the price in London, and every figure we give you follows a free survey rather than preceding it.