Polyisocyanurate

Polyisocyanurate, also referred to as PIR, is essentially an improvement on polyurethane (PUR). Different catalysts are used and the proportion of methylene diphenyl diisocyanate (MDI) is higher than for PUR. Instead of a polyether, a polyester derived polyol is used in the reaction.

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The reaction of polyol and MDI takes place at higher temperatures compared to the reaction temperature for the manufacture of PUR. As a result the MDI will also react with itself, producing strong chains of isocyanurate. These crosslinks are stronger than normal bonds in polyurethane. Therefore they are more difficult to break. As a result PIR foam is chemically and thermally more stable (disintegration starts above 400degC).

PIR typically has a MDI/polyol ratio over 400. This is defined by an ISO standard: ISO-....

PIR is typically produced as a foam. PIR is used for thermal insulation, one inch of PIR has an R value of 5.30 without any facers.