Polyurethane spray foam is a mixture of two liquid chemical compounds. The unique properties of the ingredients in the compounds, when blended, cause a reaction that results in a foam substance that quickly expands. This substance also completely seals the material, or substrate, that it has been sprayed on. The foam is thus both an air sealer and an effective insulator, making spray foam insulation the most effective option for insulating homes and buildings.
Foam insulation is blended on-site from two industrial sized drums called the A side and the B side. The A side has two ingredients that determine whether the foam produced will be open cell foam or closed cell foam. Open cell foam has a cell structure that is not closed on all sides. Open cell foam yields a very effective air barrier. Closed cell foam has a completely closed cell structure. It yields both a superior air barrier and a moisture barrier due to its closed cell structure. The B side drum is a blend of polyols, blowing agents, and a surfactant. It also holds a catalyst that engages the foaming process when it comes in contact with the A side ingredients.
The blending process of the A side and B side happens inside the spray gun that installers use to apply the foam to the substrate. The materials are pumped from their drums into separate hoses. During transport, the hoses heat up the foam to an optimal temperature for the chemical reaction to take place depending on the foam’s formulation. When both heated substances reach the spray gun, they are mixed together and the reaction occurs so that when the liquid hits the substrate, it begins to foam immediately. Foam starts to cure right away as it expands with closed cell foam taking long to cure than open cell foam. Closed cell foam will cure more firmly than open cell foam. This is why closed cell foam also makes a terrific addition to the structure of a wall or roof members and is used extensively to augment the roof structures of homes and buildings in hurricane-prone areas.
Applying spray foam is part art and part science. The art part comes into play because a technician needs to know where to spray and what pattern of spray will most effectively seal and insulate an area. The science end of things involves selecting the right formulation of foam to use for a project and getting the foam to the optimal temperature for the foaming reaction to take place. This is why spray foam insulation is not typically a do it yourself job. An experienced technician will do the job faster and more effectively than someone who doesn’t have the training. The complexities involved with the blending of the foam make it easy to ruin a job before the first joist cavities are done.