A denser spray foam with a higher R-value per inch that can also add rigidity and act as a vapor retarder in many assemblies. Often considered for exterior, structural, and moisture-sensitive applications.
Closed-cell spray foam is the denser of the two spray polyurethane foam types. Its cells are sealed rather than open, which is why the cured foam feels firm and hard rather than spongy — a noticeable difference from open-cell foam.
That denser structure carries two practical consequences. First, it provides more insulating value per inch, which matters most where cavity depth is limited — thin exterior wall assemblies, for example. Second, it is less vapor-permeable than open-cell foam, which means closed-cell foam can act as a vapor retarder in many assemblies.
Closed-cell foam also expands less than open-cell foam and builds up in layers, so thicker applications are achieved by applying passes rather than relying on a single expansion. Because of its density, it can add rigidity to the assembly it is bonded to.
None of this makes closed-cell foam the automatic answer. A vapor-retarding material in the wrong location can trap moisture rather than manage it. Where it belongs depends on the whole assembly — not just on the foam itself.
Because closed-cell foam restricts vapor movement, placement matters as much as the product. Before specifying it we consider:
The two foams behave differently, and the differences matter most when cavity depth is tight or when vapor movement needs to be managed. Here is the short version — see the spray foam insulation overview for the complete comparison.
Share the details of your building and we will walk through whether closed-cell foam is the right fit for each area.
Comparing both options? Read about open-cell foam or see our service area.