Polyurethane spray foam insulation is a mixture of liquid chemical substances that when blended, produce a reaction that foams. When the liquids come in contact with a surface, such as a wall or roof, the foam expands to hundreds of times its size. The thickness of the foam yields a high R-value, or insulating value, per inch. Foam insulation also creates a complete air seal on the substrate and can also shield against water vapor and moisture.
The liquids that are blended together to produce spray foam are known in the industry as the A side and the B side. The A side contains the substance that produces the reaction that causes the foam as well as a surfactant, a blowing agent such as water or carbon dioxide, and a catalyst that gets everything started. In the B side is where you will find the blend that determines whether the foam is open cell or closed cell and which gives the foam its unique characteristics for particular applications.
There are two main types of polyurethane spray foam insulation, open cell and closed cell. Closed cell foam is known as two pound foam or high pressure foam and not only seals out air, but is also an effective moisture barrier. This type of foam is good for areas that are mold and mildew prone such as crawl spaces and basements. Closed cell foam also cures into a hardened substance that will add strength to building materials such as roof sections and wall sections. Open cell spray foam is called low pressure or 1/2 pound foam. It also seals out air and all cracks and gaps in building materials where air can enter or escape. It also has the benefit of being a great sound insulator.
Polyurethane spray foam works by created a continuous and secure seal and can be used in both retrofit and new build applications. Because of its higher R-value per inch, it is a preferred insulation by home and building owners who are looking to save the most money and on energy consumption. A distinct advantage of polyurethane foam is that it is permanent and does not need replacing every ten or fifteen years like other insulation options.