Spray Foam Insulation R-Value

Ever Wonder What an Insulation R-Value Means?

R-value measures how strongly an insulation material resists heat flow. The higher the R-value of your insulation, the better it slows heat moving in or out of a building. Essentially, the higher the number, the better it performs. 

For spray polyurethane foam, there are two forms to consider: open-cell foam is typically around R-3.5 to R-3.7 per inch, while closed-cell spray foam is typically around R-6 to R-7 per inch, depending on the product and test method. DOE guidance places open-cell spray foam at a lower R-value than closed-cell, and recent ICC-ES product reports for closed-cell systems still commonly show values in the high-R-per-inch range.

Knowledgeable insulation contractors like Omaha Spray Foam use a combination of open- and closed-cell spray foam to adequately cover buildings. That’s because open-cell foam fits better into odd crevices, and closed-cell is easier to apply to straight, flat surfaces.

That difference matters when space is limited. If you are insulating a rim joist, crawl space wall or roofline where every inch counts, closed-cell foam provides greater thermal resistance in less depth. 

Spray foam’s advantage is that it insulates and air-seals simultaneously. DOE specifically notes that closed-cell foam provides stronger resistance to both moisture and air leakage, while open-cell foam is lighter and less expensive but should not be used below grade where it could absorb water. 

So Which Foam Gives You the “Right” R-value? 

It depends on the application. Open-cell foam is often chosen for interior wall cavities, sound control and assemblies where thickness is available. Closed-cell foam is the stronger choice when you need a thinner profile, a more robust moisture barrier or added rigidity. 

In practical terms, that means you should not compare spray foam to fiberglass or cellulose on R-value alone. Spray foam often changes the whole performance profile of the assembly by cutting uncontrolled air movement. That can mean fewer drafts, more stable indoor temperatures and less condensation risk around vulnerable surfaces.  

For homeowners and builders comparing their options, the smarter question is not “What is the highest R-value?” It is “Which insulation system gives this part of the building the best total performance?” In some assemblies, that will be open-cell. In others, closed-cell is the better fit. The right answer depends on moisture exposure, available cavity depth, target code levels and whether air sealing is already being handled elsewhere.

Omaha Spray Foam works with spray foam, fiberglass, cellulose and specialty applications across Omaha and nearby communities. If you are trying to find the best R-value, air sealing and moisture control for your project, let’s talk!