Closed Cell vsOpen Cell Spray Foam
Closed-cell or open-cell spray foam? This guide compares the two on R-value, moisture control, sound, and cost, and explains where each one belongs in a Minnesota home, so you know what you are paying for and why.
Two foams, two different jobs.
Both open-cell and closed-cell spray foam air-seal and insulate, and both outperform fiberglass batts at stopping the air leakage that drives heat loss in a Minnesota home. The difference is in their structure. Open-cell foam is light and spongy with cells that stay open, while closed-cell foam is dense and rigid with cells packed tightly shut.
That structural difference changes everything about how each foam behaves: its R-value per inch, whether it controls moisture, how it handles sound, and what it costs. Neither is better across the board. The right foam depends on the part of the house you are insulating, and the best projects often use both.
Closed-cell insulates more per inch.
Closed-cell foam delivers roughly R-6 to R-7 per inch, the highest of any common insulation. Open-cell foam runs about R-3.5 to R-4 per inch. That means closed-cell reaches a given R-value in less thickness, which is why it is the go-to where cavity depth is limited, like rim joists and basement walls.
Where there is plenty of depth to work with, such as an open wall or a vaulted roof, open-cell foam has room to reach the same R-value with more thickness, and it does so at a lower cost. The question is not which number is bigger; it is how much depth you have and what that space needs.
Where closed-cell and open-cell each pull ahead.
Closed-cell foam acts as a vapor retarder at typical installed thicknesses, so it controls moisture as it insulates. That makes it the right choice for rim joists, crawl spaces, basements, and metal buildings, where keeping warm indoor air off cold surfaces prevents condensation. Open-cell foam is not a vapor retarder, so it is not suited to those moisture-critical spots.
Open-cell foam has its own edge: its soft, open structure absorbs airborne sound very well, which makes it popular for interior walls, ceilings, bedrooms, and media rooms. It is also excellent at filling deep, irregular cavities completely. Match the foam to the priority of the space, and each one shines.
How the two compare on price.
Closed-cell foam costs more per board foot because it is denser and higher performing. These are general industry ranges for reference, not a quote from Trust Works.
These are general industry ranges for reference only and are not a price quote from Trust Works Company. The best value comes from using the right foam in the right place, which we spec during a free on-site estimate.
Most homes are better with both.
In practice, the smartest approach is rarely one foam everywhere. We reach for closed-cell foam in rim joists, crawl spaces, and basement walls where moisture control and a high R-value in a shallow depth matter, and open-cell foam in interior walls, ceilings, and vaulted roofs where air sealing and sound control are the priority and closed-cell would be an unnecessary premium.
That is how you get the best performance for the money: match each foam to the assembly rather than overspending or underbuilding. When we estimate a project, we spec the foam by area and explain exactly why, so you know your investment is going where it counts.
Frequently asked questions.
Not sure which foam you need?
We spec the right foam for each part of your project. Get a free, no-pressure estimate anywhere in Minnesota.