Open-Cell vs. Closed-Cell Spray Foam: What's the Difference?

The Basics: How They're Made

Both types of spray foam start the same way: two chemical components (an isocyanate and a polyol blend) are mixed at the spray tip of a professional gun and react almost instantly to form foam that expands and hardens in place.

The key difference is in what happens during that expansion: in open-cell foam, the cells burst open as they expand, creating a soft, sponge-like foam. In closed-cell foam, the cells remain sealed during curing, trapping an inert gas inside each tiny bubble and creating a rigid, dense foam. That fundamental structural difference drives nearly every other difference between the two products.

R-Value: Closed-Cell Wins, But Open-Cell Is No Slouch

Closed-cell spray foam delivers approximately R-6.5 per inch — significantly higher than open-cell's R-3.7 per inch. For a 2-inch application, that's R-13 vs. R-7.4. For areas where you need maximum R-value in limited space, closed-cell wins.

However, open-cell foam is applied in much greater thickness for a lower cost, so when space isn't a constraint (like an open attic floor or large wall cavities), open-cell can achieve very high total R-values. A 5-inch open-cell attic application delivers about R-19 — sufficient for most Florida climate zone requirements.

Moisture: The Critical Difference for Florida

This is arguably the most important factor for Florida homeowners. Closed-cell spray foam at 2+ inches is a Class II vapor retarder — it physically prevents moisture vapor from passing through your wall assembly. This is critical in any coastal or flood-prone area, and anywhere that exterior moisture intrusion is a risk.

Open-cell foam is permeable — moisture vapor passes through it. In most interior applications, this is actually an advantage: it allows any moisture that does get into the wall cavity to dry out rather than being trapped. This is why open-cell foam is popular for interior applications in Florida's mixed humidity climate. For exterior walls and roofs, where you want to stop moisture at the boundary, closed-cell is the clear choice.

Which Type Is Right for Your Naples Home?

Can You Use Both in the Same Home?

Absolutely — and this is often the most cost-effective approach. A common strategy for Naples homes is to use closed-cell foam on the roof deck (for hurricane protection and moisture barrier) and open-cell foam on interior walls and in attic floor cavities (for cost-effective air sealing and soundproofing). Our team can assess your specific home and recommend the optimal combination for your goals and budget.