Polyurethane (PUR) and PIR foam
Also known as: PUR, PIR, polyisocyanurate
Short definitionThe closed-cell rigid foam that fills the space between the two metal sheets of a cold room panel. Its thermal conductivity is around 0.022 W/mK; the PIR type resists fire better.
The foam forms when polyol and isocyanate react and expand in the panel mould. The result is a closed-cell filling of about 40 kg/m³ density that does not take up water. Its thermal conductivity of 0.020–0.024 W/mK beats rock wool and EPS; the same insulation is achieved with a thinner panel. Because the sheet is bonded to the foam, the panel both insulates and carries load.
The first question in a quote is PUR or PIR. In a fire PIR chars on the surface and slows the flame, and it reaches up to class B-s1,d0 under EN 13501; it is asked for in large warehouses and where the insurer requires it. The insulation value of the two is almost the same. When buying panels, check that the foam has no voids, that the sheet does not separate from the foam and that the joints are true. As foam ages its insulation drops a little.