Expanding foam is a useful tool for both home repair do-it-yourselfers and professional builders. It expands to fill a space, moulding itself to the shape of the cavity it fills to create a better seal. Inside the foam are tiny trapped bubbles of air that help to create an insulating layer, preventing heat from easily flowing through the foam.
Polyurethane foam is a common choice for home do-it-yourselfers. It cures into a rigid form that can be easily shaped or sculpted with a bread knife. It comes in a low-expansion single-component form used to seal windows, openings for pipes and wires and other minor gaps. Single-ingredient polyurethane has a low R-value, however, which makes it a poor insulator. Two-component polyurethane foam, insulates better and can be used as both an insulation and a sealant. With the exception of special low-expansion formulas, polyurethane expands to about 200 per cent its original area, which can cause it to warp windows and other spots if it is not applied carefully. Use it cautiously, since it is extremely difficult to remove from your skin or clothes.
Latex foam is an alternative to polyurethane. It comes in aerosol cans that make it simple to spray into gaps and cracks to produce a tight seal. It only expands 75 per cent, which makes it a bit easier to work with in tight space than polyurethane. Unlike polyurethane, which can only be worked when dry, latex can only be worked when it is wet. It also cures to a different texture, remaining soft and pliant. It cleans up easily with soap and water, giving it an advantage over polyurethane for messy jobs.
Polyisocyanaurate is a spray foam used extensively as insulation. It comes both as a spray expanding foam and rigid panels, but is usually used as a spray since it is cheaper and more efficient when it is just sprayed in place. In most respects, it is similar to polyurethane, but has a higher R-value, making it an extremely effective insulator. It does drop somewhat over the first two years as some of the trapped gas bubbles escape from the foam and are replaced by less efficient air bubbles. After two years, however, the polyisocyanaurate stabilises and stops losing insulating value.