Foam insulation, usually urethane, can be injected into wall cavities or sprayed onto roof or floors. Once applied, it expands and sets in about a minute. After it sets, it shrinks slowly for several weeks. Properly applied, shrinkage is less than 5 percent. Like rigid boards, foam insulation has the advantage of high R-value per inch. Similarly, it shares the disadvantage of requiring a fireproof covering material when installed inside the home.

New foam products on the market are showing improved shrinkage and flammability characteristics. Consider for example, Icynene® Spray Foam. It has no reported shrinkage characteristics and is Class A fire rated, meaning it can be used in attics and requires no covering. Take the time to speak with your local insulation contractor to determine the insulation method best suited for your budget, home and climate area.