Closed-Cell vs. Open-Cell Spray Foam: Which One Do You Need?

What Actually Makes Them Different

Both open-cell and closed-cell spray foam start from similar two-part liquid chemistry, but the cell structure that forms during expansion is what separates them. In open-cell foam, the tiny cells that form during expansion stay open and interconnected — like a sponge — which keeps the foam light and soft but lets air and vapor move through it more easily. In closed-cell foam, those cells form as sealed, individual pockets, which makes the foam denser, more rigid, and resistant to moisture passing through it. For general background on how spray foam expands and cures in the first place, see our full spray foam insulation guide.

Side-by-Side Comparison

R-Value Difference

Closed-cell foam's tighter, gas-filled cell structure gives it close to double the R-value per inch of open-cell foam. In practice, that means a wall cavity insulated with closed-cell foam can hit a higher R-value at a shallower thickness than the same cavity filled with open-cell foam — which matters in tight framing like a 2x4 wall where every fraction of an inch counts. See our full breakdown of what R-value actually measures for more on why this number alone doesn't tell the whole story of how a wall performs.

Moisture & Vapor Resistance

This is where the two types diverge the most. Open-cell foam lets water vapor pass through it, which is fine in many interior wall applications but a problem in spaces where moisture control is the whole point — a crawl space or a rim joist, for example. Closed-cell foam, sprayed at a sufficient thickness, can function as a vapor barrier in its own right, which is why it's the default choice for crawl space encapsulation and similar moisture-sensitive applications.

Structural Strength

Closed-cell foam's density gives it real structural value — it can add meaningful racking strength to framed walls and is often used specifically to stiffen a structure, not just insulate it. This matters more in applications like pole barns and metal buildings, where the foam is sometimes doing double duty as both insulation and a bonding layer against the metal panel. Open-cell foam doesn't offer a comparable structural benefit.

Sound Dampening

Open-cell foam's soft, open structure absorbs sound waves more effectively than closed-cell foam's dense, rigid structure, which is why open-cell is the more common choice in interior partition walls where noise transfer between rooms is a concern — a home theater, a shared wall between a bedroom and a laundry room, or an office wanting some acoustic separation.

Cost Difference

Closed-cell foam costs more per square foot than open-cell — generally due to its denser formulation and the added moisture resistance and R-value it delivers. For a full breakdown of current pricing for both types, see our spray foam cost per square foot guide.

Can You Use Both in One Project?

Yes, and it's common practice rather than an exception especially in certain Kansas climates. A typical residential job might use closed-cell foam on the rim joist and crawl space walls, where moisture control matters most, while using open-cell foam on the interior wall cavities and attic floor, where cost efficiency and sound dampening are more relevant. Matching foam type to the specific demands of each area of a building including a farmouse in Kansas, rather than using one type everywhere, is generally the more cost-effective approach.

Fire Safety Considerations

Both foam types are combustible in their raw form and require an ignition or thermal barrier — commonly drywall — between exposed foam and occupied space under most building codes. Neither type is inherently safer than the other on this point; the code requirement applies regardless of which foam is used. For more on this and other code considerations, see the building codes section of our full spray foam guide.

785 Insulation Editorial Team

Spray Foam Insulation Contractors

Frequently Asked Questions