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High density polyisocyanurate insulation

Polyisocyanurate (also known as polyiso or PIR) is essentially an improvement on polyurethane (PUR).

The proportion of methylene diphenyl diisocyanate (MDI) is higher than for PUR and instead of a polyether polyol, a polyester derived polyol is used in the reaction. Catalysts and additives used in PIR formulations also differ from those used in PUR. Advantages of polyisocyanurate over polyurethane are...
  • Higher R-value per inch of thickness
  • Greater stiffness and dimensional stability
  • Better compressive strength
  • Superior performance in fire tests
PIR insulation is typically produced as a foam and used as rigid thermal insulation. Its thermal conductivity has a typical value of 0.16 BTU*in/hr*ft2*°F (0.023 W/mK).


The widely used "R-value" measurement simply refers to thermal "resistance value" - that is, a measure of insulation's ability to impede heat flow, thereby keeping hot or cold air outside. A higher R-value means that insulation works more efficiently. Increasing the thickness of an insulation layer increases R-value.

R-value Comparison of Common Insulation Materials

Polyiso is the most thermally efficient rigid insulation available in the marketplace; it has the highest R-value per inch of thickness. Because of its superior R-value, buildings that use Polyiso have lower heating and cooling costs than buildings insulated with other materials of the same thickness. For every three and a half inches of polyiso foam (R27), this much of another insulating material would be needed for equivalent insulatin performance:

Insulation Material R-value Range Thickness to Match 3.5" of PIR
PIR (Polyisocyanurate) R 7.6 - 8.0/inch 3.5inches
PUR (Polyurethane) R 5.6 - 6.0/inch 4.7 inches
Polystyrene R 3.8 - 5.0/inch 6.2 inches
Cellulose R 3.6 - 3.8/inch 7.4 inches
Fiberglass R 2.9 - 3.8/inch 8.1 inches
OSB Sheathing R 1.25/inch 21.8 inches
Plywood R 1.25/inch 21.8 inches
Concrete Block R 0.25/inch 109.2 inches
Brick R 0.2/inch 136.5 inches

Fire resistance

Polyiso meets the strict standard of both FM Class 1 Approvals (FM 4450/4470), UL 1256, and CAN/ULC S126M

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