UK · Updated 2026 · How-to
How to Tell if PIR Insulation is Water Damaged
PIR insulation that got wet on site is worthless — the foil delaminates, thermal performance drops 15–25%, and mould colonises the closed-cell foam. Six tests separate good surplus from bin material.
The six checks
- Foil bond: press hard — it shouldn't lift
- Weight: dry PIR is featherlight for its size
- Smell: musty = wet, wet = reject
- Edge: closed-cell should look uniform, no bubbles
- Corners: crumbling = compressed and wet
- Sound: dull tap = wet core
What to do if you buy some wet
Return politely with photos. Reputable sellers will refund. If not, wet PIR is safe to compost only in tiny quantities — most goes to landfill.
Frequently asked questions
+Can wet PIR be dried out?
No. Once water penetrates the closed cells, thermal performance is permanently reduced.
+Is stained foil always bad?
Not always — light staining from rain runoff is cosmetic. Deep brown or green staining means prolonged wet.
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