Insulation material guide
Material classes described by what they are and where they normally suit. No brands, no products, and no performance figures, because those vary by specification rather than by class.
| Material class | Usual form | Normally used at | Limiting factor |
|---|---|---|---|
| Mineral fibre batt | Semi-rigid batt or roll | Between joists, studs and rafters | Needs a friction fit; performance falls off sharply with gaps |
| Loose fill | Blown or poured granules or fibre | Open horizontal roof spaces | Settles and cannot be used on a slope |
| Rigid foam board | Faced or unfaced boards | Continuous layers over or under structure | Joints must be sealed; unforgiving of an uneven substrate |
| Wood fibre board | Rigid or flexible board | Vapour-open internal and roof build-ups | Thicker for the same reduction; must be able to dry |
| Sheep wool and other natural fibre | Batt or roll | Between timbers where vapour openness matters | Handles moisture well but needs protection from pests |
| Blown cellulose | Dense-packed fibre | Closed cavities and stud bays | Requires the cavity to be genuinely closed and access holes made good |
| Reflective multifoil | Thin layered foil | Where an adjacent air gap can be guaranteed | Depends entirely on a maintained air gap and a clean surface |
Scroll the table sideways for the remaining columns.
Notes on using this sheet
- Class describes form and behaviour, not a specification. Two products in the same class can differ substantially.
- Any class installed with gaps performs closer to no insulation than to its intended value, which is why fit matters more than class in most retrofits.
- Whether an assembly can dry is a property of the whole build-up, not of the insulation alone.