Closed-cell spray foam is a dense, rigid polyurethane foam insulation with tightly packed closed cells, providing higher R-value per inch of thickness and genuine moisture resistance compared to open-cell alternatives, along with some structural rigidity contribution to the assembly it’s applied within.
This dense cellular structure makes closed-cell foam essentially impermeable to moisture vapor, a genuine advantage for below-grade applications, roof assemblies, or any location where moisture resistance is a particular priority beyond simple thermal performance.
Because closed-cell foam achieves higher R-value in less thickness than open-cell alternatives, it’s often preferred for applications with limited cavity depth where maximizing thermal performance within a constrained space matters significantly.
What Does Closed-Cell Spray Foam Involve?
- Tightly packed closed cells providing moisture resistance
- Higher R-value per inch than open-cell alternatives
- Rigid structure contributing some assembly strength
- Generally higher cost per board foot than open-cell foam
Why Is Closed-Cell Spray Foam Important?
The genuine moisture resistance and higher R-value per inch closed-cell foam provides makes it particularly valuable for below-grade applications, roof decks, and other locations where moisture exposure or limited space demand these specific performance characteristics beyond what open-cell foam or standard insulation could offer. This targeted suitability justifies closed-cell foam’s higher cost for these particular high-performance applications.
Because closed-cell foam’s rigid structure can also add meaningful racking strength to a wall assembly, some structural engineers specifically account for this contribution in certain applications, though this benefit shouldn’t be assumed without proper engineering verification for load-bearing considerations. This higher investment is often well justified given the specific performance demands of these applications. This willingness to invest more upfront often pays off through superior long-term performance.
Closed-Cell Spray Foam vs. Open-Cell Spray Foam
Closed-cell spray foam offers higher R-value, moisture resistance, and some structural contribution at higher cost. Open-cell spray foam provides lower cost and better sound dampening, with vapor permeability suited to different application needs.