When discussing spray foam insulation, there are two main types commonly referred to as Open Cell and Closed Cell. Understanding the differences between them makes it easier to make an informed choice about which to use. Open cell foam is softer and less dense with air pockets within the cell structure of the foam. The density of the foam is measured by lb. per cubic foot. Open cell foam has a density of 0.5lb/cu.ft. The R-value (measure of resistance to heat flow) of open cell is typically around 3.5 to 4 per inch. Open cell foam is a good choice for most wall, attic, and soundproofing applications.
Closed cell foam differs in that its cell structure is closed and packed tightly together making it much denser and hard to the touch. Density measures in at 2.0lb./cu.ft. Because it is so rigid, closed cell can actually improve the structural stability of a building and is routinely used in some storm prone areas for added strength. Closed cell products have an R-value of 6-7 per inch. This makes them extra efficient. Closed cell also creates a seamless moisture barrier making it ideal for use under subfloors and crawlspaces as well as walls and attics.
Both types of foam create an air seal, inhibit moisture buildup and mold and are excellent insulators. While closed cell is more expensive than open cell, the specifications of the project sometimes require the extra R-value, structural rigidity, and moisture barrier of a closed cell product.