Types of Roof Insulation Boards

Commercial roofing assemblies use various types of insulation boards. Understanding each type helps building owners evaluate roofing system options and performance claims.

Polyisocyanurate (Polyiso)

The most widely used commercial roofing insulation. Nominal R-value: R-6.5 per inch. Key limitation: R-value degrades significantly in cold temperatures (can drop to R-4 or lower below 20°F). Cost-effective and widely available. Most common in TPO and EPDM roofing assemblies.

Expanded Polystyrene (EPS)

R-value: R-4 per inch, consistent across temperature ranges. Doesn't absorb moisture significantly. Better cold-climate performance than polyiso. Used when consistent R-value across temperature ranges is important.

Extruded Polystyrene (XPS)

R-value: R-5 per inch, consistent across temperature ranges. Excellent moisture resistance. Premium cost vs. EPS or polyiso. Best where moisture exposure is a concern.

Mineral Wool (Rock Wool)

R-value: R-4 per inch. Fire-resistant, does not contribute to flame spread. Used in applications requiring fire resistance. Heavier than foam boards.

Spray Polyurethane Foam: The Superior Alternative

Spray foam (R-6.5/inch, consistent across temperatures) outperforms all board insulation options in several ways: no seams at board joints (eliminating thermal bridging), no separate coverboard required, directly bonds to substrate, and simultaneously provides insulation AND waterproofing. For most commercial roofing restoration applications, spray foam delivers better performance than any board insulation system.