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Closed Cell vs. Open Cell

When it comes time to actually put the
foam product in your home or commercial
building structure, you must identify whether
you will use open cell foam, or closed cell
sprayfoam. This decision can make a big
difference in cost, application methods,
and performance.

What is the Difference between Open-cell and Closed-cell Polyurethane Foams?

There are two major factors to understand and consider with the open-cell vs. closed-cell issue. The first is the nature of the foam. It is either open-cell foam, where the tiny cells of the foam are not completely closed. They are broken and air fills all of the open space inside the material. This makes the foam weaker or softer-feeling than closed-cell foam.

Closed-cell foam differs in that all of its tiny foam cells are closed and packed together. They are filled with a gas that helps the foam rise and expand and become a greater insulator. These cells can be formulated to obtain many characteristics, the most common being size and density.

Foam density is measured by weighing one solid cubic foot of foam material. Open cell foams typically weigh in at 0.4 to 0.5 lb./cu. ft. Closed cell foam for insulation applications range in density from 1.7 lb./cu. ft. to 2.0 lb./cu. ft. Commercial roofing applications typically use a 2.8 to 3.0+ lb./cu. ft. to support traffic and loads better, and never use open cell foam products. The higher the density the foam, the heavier, or stronger it becomes.

The advantages of closed-cell foam compared to open-cell foam include its strength, higher R-value, and its greater resistance to the leakage or permeance of air or water vapor. The only real disadvantage of the closed-cell foam is that it is denser, requires more material, and therefore, is more expensive. Even though it has a higher R-value, typically the cost per R is still higher than open-cell foam. The choice of foam can also be based on the requirements for the other performance or application specific characteristics such as strength, vapor control, available space, etc. Open-cell SPF has an R-value around 4.2 per inch and typically uses water as the blowing agent. Closed-cell SPF has an R-value of around 6.7 per inch (aged R-value) and uses high R-value blowing agents.

Both open and closed cell foams are commonly used in most building applications and the choice of which to use can depend on many of the factors discussed above. Some foams are inappropriate in specific applications. For example, you typically would not use open-cell foam below grade or in flotation applications where it could absorb water; this would negate its thermal performance because water is a poor insulator compared to air. Closed-cell foam would be a good choice where small framing sizes need the greatest R-value per inch possible. Closed-cell foam would be used for roofing applications.

What type of foam being used in your building or home is always a good issue to discuss with your spray foam installation professional up front, before the job starts.