Polyisocyanurate (PIR) boards are an improved type of Polyurethane (PUR) foam and are proven to have excellent thermal insulation properties. It has high resistance to moisture absorption, resulting in anti fungi growth. These high-quality CFC-free PIR boards are lightweight, hence putting less load on the structure. The proportion of methylene diphenyl disocyanate (MDI) is greater and a polyester-derived polyol is used in reaction instead of a polyether polyol. This reaction is achieved at higher temperatures which creates strong isocyanurate linkages in the molecular structure. These linkages are much stronger than the normal linkages in the PUR foam, and much more difficult to break, hence making PIR foam chemically more stable.