is the Difference between Open-cell and Closed-cell Polyurethane Foams?
it comes time to actually put the foam product in your home or commercial building structure, you must identify whether you
will use .05 lb./cu. ft., open cell foam, or 2.0 lb./cu. ft. closed cell foam. This makes a big difference in cost, application
methods, and performance.
With the open-cell vs. closed-cell issue, there are two
major factors to understand and consider. 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.
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.
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. Roofing applications typically use a 2.8 to 3.0+ lb./cu. ft. to support
traffic and loads better. The higher the density the foam, the heavier, or stronger it becomes. Some polyurethane foams are
molded into decorative interior molding and painted or stained for a simulated wood effect. These “higher density”
foams are typically in the 30 lb./cu. ft. to 40 lb./cu. ft. density range.
The advantages of closed-cell foam compared to open-cell foam include its strength, higher R-value,
and its greater resistance to the leakage of air or water vapor. The disadvantage of the closed-cell foam is that it is denser,
requires more material, and therefore, is more expensive. Even though it has a better 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
3.5 per inch and typically uses water as the blowing agent. Closed-cell SPF has an R-value
of around 6.0 per inch (aged R-value) and uses high R-value blowing agents.
Both types of foam are commonly used in most building applications and the choice for 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.
Always contact your material supplier for performance and
application data on their specific materials. What type of foam being used in your building or home is always a good issue
to discuss up front, before the job starts.