PIR insulation
PIR (polyisocyanurate) is a high-performance closed-cell rigid board, about double the R-value of glasswool for the same thickness, usually foil-faced.
Ask Chalkline about this →PIR insulation is polyisocyanurate rigid foam: a high-performance closed-cell board, around R0.5 per 10 mm (roughly double the R-value of the same thickness of glasswool), usually faced with foil. It is used where high R-value is needed in limited depth and where better fire performance matters.
PIR is a step up from polystyrene foams on two fronts:
- R-value per millimetre: its thermal conductivity is low, so for a given thickness it delivers roughly twice the R-value of bulk glasswool. That makes it valuable where depth is constrained, a thin wall build-up, a flat roof, a continuous-insulation layer over framing.
- Fire performance: PIR chars rather than melting and dripping the way some foams do, and faced products can achieve good early-fire performance, which is why it is often chosen where surface fire spread is a concern.
The foil facing serves two purposes: it protects the foam and, where it faces an air gap, adds a reflective component to the assembly’s R-value.
For a builder the practical points are to use PIR where the R-value-in-limited-depth or the fire properties justify its higher cost over glasswool or EPS, to keep the foil facing intact (damage it and you lose the reflective benefit and expose the foam), and to seal board joints so the high R-value is not undone by air movement around the boards. As with any closed-cell board, mind the vapour position in the assembly and detail to the NCC condensation provisions for the climate zone.
Also known as: Polyisocyanurate, PIR board.
Category: Insulation / Materials.
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References
- Rigid foam (Chalkline) (verified 2026-06-01)
Last updated: 2026-06-01. Verified: 2026-06-01. Quarterly review for currency.