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 per inch. Similarly, it shares the disadvantage of requiring a fireproof
covering material when installed inside the home.
