Multifoil loft insulation
Thin, flexible blankets of foil layers separated by wadding or foam. Multifoils work partly by reflecting heat, which means how they are fitted matters as much as the product.
| What it is | Several reflective foil layers with thin wadding or foam between them |
|---|---|
| Comes as | Flexible rolls, usually a few tens of millimetres thick |
| How it works | Reflects radiant heat, and traps still air, especially with air gaps either side |
| Fitted | Stapled across rafters or joists, with joints taped |
| Best for | Roof slopes and tight spaces, often combined with other insulation |
How multifoil works
Most insulation works by trapping air in fibres or foam. Multifoil does that too, but much of its effect comes from shiny surfaces reflecting heat back. Reflective surfaces only work well when they face an air gap, so multifoil is usually fitted with a small, still air space on one or both sides. Fitted tight against other materials, it does much less.
Where it’s used
Multifoil is mostly used in the slope of the roof, often in loft rooms, outbuildings and roofs where there is little depth, and frequently in combination with rigid boards or rolls. It also acts as a vapour control layer in some designs. For a standard cold loft with depth to spare, rolls laid on the floor are simpler and cheaper.
What to check
- Look for products with independent certification for the way they will be installed
- Ask how the air gaps will be created and kept the product relies on
- Joints and edges need to be taped to keep air from getting round
- If it is going in the roof slope, ask how the roof will be ventilated
Common questions
Is a thin multifoil as good as thick loft rolls?
Can multifoil go on the loft floor?
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