Polyisocyanurate

Polyisocyanurate is a thermoset plastic. It is also called PIR, polyiso, or ISO. It is usually made as a foam. It is used as rigid thermal insulation. It is similar to polyurethane (PUR) except that the proportion of methylene diphenyl diisocyanate is higher and a polyester-derived polyol is used in the reaction instead of a polyether polyol.  Catalysts and additives used are also different from those used in PUR.

 References 

Other websites

Polyisocyanurate Insulation Manufacturers Association 
Polyisocyanurate Insulation energy savings, by Center for the Polyurethanes Industry 

Category:Polymers