Open Cell vs. Closed Cell Spray Foam: Side-by-Side Video Comparison

"Open cell or closed cell?" is one of the first real decisions in any spray foam project, and the two types perform differently enough that the choice matters. Here's a direct, side-by-side comparison.

Density and Structure

Open-cell foam has a softer, spongier structure — the cells within the foam are intentionally left open, which is why it's lighter and more flexible. Closed-cell foam has a denser, rigid structure where the cells are fully closed, trapping gas inside each cell, which is what gives it higher R-value and structural properties.

R-Value Per Inch

This is the most commonly cited difference: closed-cell foam typically delivers roughly double the R-value per inch compared to open-cell. In practice, this means closed-cell can hit a target R-value in a much thinner application — relevant in tight cavities or when maximizing usable interior space matters.

Vapor Permeability

Open-cell foam is vapor-permeable, meaning moisture vapor can pass through it — which can be an advantage in certain wall assemblies where the design intends for some moisture movement. Closed-cell foam acts as a vapor barrier, blocking moisture movement almost entirely — a real advantage in some applications (like below-grade or high-moisture environments) and a real risk in others if it traps existing moisture on the wrong side of the assembly. This is exactly the kind of detail worth having an experienced installer assess for your specific structure.

Cost

Closed-cell foam generally costs more per board-foot than open-cell, driven by both the material itself and the higher density applied. For a given cavity, closed-cell will typically cost more to fill than open-cell, though it may allow a thinner (and therefore sometimes cheaper overall) application to hit the same R-value target.

Best Use Cases

Open-cell tends to be favored for: interior wall cavities where sound dampening is a bonus, larger volume fills where cost efficiency matters, and applications where some vapor permeability is desired by design.

Closed-cell tends to be favored for: roof decks and attics (where its vapor-barrier properties and high R-value per inch matter most), below-grade and crawl space applications (moisture resistance), and any application where added structural rigidity is a genuine benefit.

Seeing the Difference

Manufacturer equipment and application demonstrations — the kind found in our Application & Installation Videos hub — illustrate the visual and textural difference clearly: open-cell expands into a lighter, more porous fill, while closed-cell sets into a denser, more rigid surface. Watching both in action makes the distinction much more concrete than a spec sheet.

Which One Is Right for Your Project?

The honest answer depends on the specific application — roof deck vs. wall cavity, climate, moisture exposure, and budget all factor in. Get matched with a vetted, insured spray foam contractor who can assess your specific project and recommend the right type.