Spray foam insulation is a composite material formed when two chemicals (isocyanate and polyol resin, typically) meet. Kept in two separate hoppers or tanks and transported by gas pressure or a liquid, these chemicals meet at the tip of a spray gun. When they meet, they react to each other and create a foam solution. This foam then dries in place and creates an effective air and vapor barrier.
 

The foam expands and hardens to fill the empty areas of your walls, floors, and ceilings. This means it fills small gaps and crevices that make it difficult for heat energy and sound to pass through the foam. And, since the foam expands to the space in which it’s sprayed, these pockets will reach even the small gaps. These characteristics make spray foam a very effective insulator.