The importance of distinguishing between the two types of spray polyurethane foams cannot be understated. When it comes time to insulate your home or commercial structure, you must decide on opting for open-cell foam. Each type of foam distinctly impacts the cost of a project, as well as the application methods and ongoing performance.
There are two major factors distinguishing closed-cell and open-cell foams: structure and density. The structure of open-cell foam consists of tiny bubbles or cells that aren't fully encapsulated - they are broken, torn, ripped, holey, etc. Because they're broken, air fills the "open" space inside the foam, which results in a soft, spongy material. Closed-cell foam differs in that every bubble or cell that makes up the foam is completely encapsulated and packed tightly together. The bubbles aren't filled with air, but rather a gas that aids foam expansion and insulative properties. This results in an altogether harder, stronger material, relative to open-cell foam.
When it comes to foam density, measurements are made by weighing one cubic foot (cu. ft.) of foam material. Closed-cell foam is roughly four times as dense as open-cell for insulation applications. Open-cell tends to be roughly 0.5 lb./cu. ft. in density, whereas closed-cell can range from 1.7 to 2.0 lb./cu. ft. in density.
Relative to open-cell foam, closed-cell foam is greater in strength, higher in R-value, and more resistant to the transmission of air and water vapor. Because closed-cell foam is denser, however, it requires more material per unit volume than open-cell, and is therefore more expensive to install - even if comparing the cost-per-R-value.
The deciding factor for going with either open-cell or closed-cell foam is also frequently based on performance or application-specific characteristics like the impact on structural integrity, control of water vapor, and the amount of available space to install the foam.
A way to denote a material's insulating properties is known as R-value, and the higher the number per unit thickness, the better an insulator a material is. Closed-cell spray foam has an R-value of about 6.0 per inch (R-6), while open-cell SPF comes in at roughly R-3.5. The blowing agent, which aids in forming the bubbles or cells that make up SPF's foam structure, is usually water for open-cell and high-R-value chemicals for closed-cell.
In addition to the situation-specific considerations mentioned above, there are more general considerations to make when deciding between open-cell and closed-cell foam. For instance, open-cell is typically inappropriate for below-grade applications or flotation applications where it could absorb water. Also, closed-cell foam would be there optimum material for roofing applications or wall insulation applications that need the greatest R-value per inch.
Of course, it's a good idea to discuss the type of foam for your project with your SPF installation professional prior to the job beginning. Also, it's always prudent to contact a supplier for complete performance specifications and application information for their line of materials.