What Kind of Spray Foam Do Roofers Use?

There are two main types of spray polyurethane foam: open-cell and closed-cell. For roofing applications, only one is appropriate.

Open-Cell vs. Closed-Cell Foam

Open-cell foam is soft, spongy, and has a lower R-value (approximately R-3.7 per inch). It absorbs water and is not waterproof — making it completely unsuitable for exterior roofing applications. It's used primarily for interior sound dampening and air sealing in walls and attic spaces.

Closed-Cell Foam: The Only Roofing Option

Closed-cell spray polyurethane foam has a rigid, dense structure with cells that are completely sealed. This makes it: waterproof (it doesn't absorb water), structurally rigid (compressive strength of 25–60 PSI), an excellent insulator (R-6.5 per inch), and a vapor barrier. These properties are essential for a roofing application that must withstand UV exposure, rain, wind, foot traffic, and temperature cycling.

Roofing-Grade Formulations

Not all closed-cell foam products are identical. Roofing-grade SPF products are specifically formulated for exterior applications and tested to meet roofing-specific performance standards. Contractors must use manufacturer-approved products to qualify for a warranted system.

The Topcoat Requirement

Regardless of foam density, spray foam for roofing always requires a protective topcoat — typically silicone or acrylic — applied immediately after the foam. The topcoat provides UV resistance and maintains the waterproofing integrity of the system.