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Home | Spray Foam 411 | Fundamentals Of Open- And Closed-Cell Foam
Open-cell spray foam is intended as cavity insulation inside exterior and interior walls, and for use in attics and crawlspaces.

Fundamentals Of Open- And Closed-Cell Foam

By Robert Naini

In the world of spray foam, there are two categories of products: open-cell and closed-cell foam. Open-cell and closed-cell spray foam insulation products are regularly used on many different types of projects in commercial, residential, industrial applications, and on various substrates such as wood, metal, and concrete.


Open-cell spray foam is referred to as semi-rigid or low-density, because it is typically less than one pound per cubic foot. Open-cell products typically use water as the blowing agent, have R-values ranging from R-3.5 to R-4.5 per inch, and have completed acoustic testing that show sound ratings up to STC 52, which translates to excellent sound attenuation properties.


Closed-cell foam, on the other hand, includes an array of products used for interior and exterior insulation and roofing applications (an additional subset of the closed-cell foam market is referred to as medium-density foam and is primarily used for interior and exterior insulation). In general, closed-cell foam is typically 1.7 to 2.5 pounds per cubic foot density and uses a non-ozone depleting blowing agent called 245fa. The density and the blowing agent have a direct affect on the R-value of spray foam, and current R-values range from R-5.5 to R-7.4 per inch, depending on the thickness of the application. Closed-cell foam is rigid, has low vapor permeance properties, and can be exposed to weather during a typical construction timeframe.


Comparing open-cell and closed-cell foam, we find that both products are spray applied in a similar manner and use the same plural component proportioning equipment. They also both provide insulation and air barrier qualities in a single application. However, the differences are important to understand, especially when deciding which product is best for a specific application.

While both products are spray applied, open-cell foam will expand over 100 times its liquid volume, whereas closed-cell foam will expand about 30 to 40 times its volume. This directly impacts minimum thicknesses of these products: open-cell foam will typically be sprayed about 2½ to 3 inches minimum, while closed-cell foam will be sprayed about 3/4 to 1 inch minimum. There are no maximum per-pass thickness limits for open-cell foam, but closed-cell foam is generally limited to about two inches per pass. For greater total thicknesses, additional passes can be sprayed after a cool-down period (refer to manufacturer data for limitations on specific products).

Originally designed in Canada for use in bonus floor applications, open-cell spray foam has expanded its reach over the past 20 years into retrofit projects, custom homes, the production builder market, and commercial construction. Open-cell foam is intended as cavity insulation inside exterior and interior walls, and for use in attics and crawlspaces. These products are not designed for structural use, are not flotation foams, and are not designed for contact with bulk water. If any of these concepts are design parameters, then closed-cell foam is the product of choice.

Closed-cell spray foam can serve as a five-in-one application by providing exterior insulation, an air barrier, a vapor retarder, a drain plane, and a water-resistive barrier in a single application. Closed-cell foam has also been tested to increase the racking load of wall assemblies for structural support, and to increase roof uplift resistance for structures in hurricane and tornado zones. It also functions as a water-resistive barrier. Furthermore, closed-cell foam can come in contact with the exterior elements and can be left exposed during a construction timeframe with no thermal degradation.

All in all, both open-cell and closed-cell foam belong to the same world of spray foam, and spray foam is a very forgiving building product, allows for flexibility in design, and provides a solution for complicated situations. The air barrier qualities of spray foam have created differentiation in the insulation market and have allowed advanced designs to be incorporated into building codes. While closed-cell foam is regularly used in residential construction as cavity wall insulation and in attics and crawlspaces, it is also becoming integral to commercial building design due to its versatility.

Considering the efficiency of designs using spray foam, the increasing demands of the energy code, including continuous insulation, and the capability to provide multiple control layers in a single application, both open-cell and closed-cell spray foam insulation will be in high demand as the construction industry continues to strive for energy excellence.


Robert Naini has a Bachelor’s of Science in Mechanical Engineering and an MBA from the University of Texas in Arlington. With more than a decade of experience on the cutting edge of spray foam insulation, Robert has developed a unique knowledge base including employee & applicator training, building code awareness, and spray foam sales & marketing. Using this knowledge, Spray Foam Advisor is developing a web-based Educational Training Program for the spray foam industry with videos, blogs, and more at

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