Open vs Closed Cell Foam Insulation

What is the difference between open and closed cell foam insulation?

Spray Foam is categorized into two types, "open-cell" or "closed-cell”. Open cell is lightweight foam that is flexible, and an excellent air barrier. Open cell foams most commonly range from .5 lb to .7lb densities. Closed cell foam is higher density foam, and a moisture barrier. Most closed cell foam used for insulation range from 1.7 lb to 2 lb. Closed cell foam can go up to 3 lb density which is often used in exterior roof applications (like the Superdome).

The main differences between open and closed cell foam are moisture permeability, R-Value, and flexibility. Closed cell foam is a moisture vapor barrier. What this means is that it will not allow moisture to pass through the foam. Open cell foam is not a moisture vapor barrier, and will allow moisture to pass. Closed cell has a higher R-value than open cell. R-value should not be the determining factor when it comes to spray foam see R value versus Performance value. Closed cell foam is around, 6.6 per inch as compared to 3.8 per inch in open cell. However, both foams are air barriers, and it is the air barrier that makes foam such an excellent insulation.

Closed cell foam is much more expensive than open cell foam.

Closed cell foam is more rigid.

So which foam is best? The best foam to use should be determined by the application. Some spray foam contractors recommend closed cell foam in some applications since their open cell foam tends to absorb moisture. All foams are not created equal. In some applications, open cell foam with a vapor retarding paint is the best application.

Closed cell foam should never be used on wooden roof decks. Moisture will be trapped in the roof's wood decking if you were to apply closed cell foam to the underside of the roof of a home and the roof develops a leak. This can lead to rotting of the roof deck before the roof leak is ever discovered. Open cell foam is not a vapor barrier, so it allows the water from the roof leak to weep through the foam to the space below so it is the better choice for most residential applications.

In most applications, the buildings energy performance will be the same regardless whether you used open or closed cell foam. Open cell foam is more flexible than closed cell foam. When the framing members expand and contract with the weather, or are impacted by high winds, open cell foam will flex with the structure. Closed cell foam however, will not flex, a will get hairline cracks where it was connected to the studs and walls and lose some of its benefits.

Open cell foam is usually more suitable for residential applications because of its moisture permeability, or the ability for moisture to pass through the insulation. (See above) Most homes are constructed out of wood, and it is this reason, moisture permeability, that is the main reason why open cell foam is best suited for your home.

Closed cell foam is best used in refrigeration, marine, industrial, and roofing or, when we are trying to solve a moisture problem and the problem can't be solved with a vapor retardant paint. Closed cell foam is commonly found outdoors.