Although spray-foam insulation is generally used when the wall-board or plaster has been stripped from the framing, it can be applied under other conditions, too. Icynene's Pour Fill insulation, for instance, is injected into the stud cavity through 1-inch holes; the material expands to 60 times its original size, giving a 2x4 wall an R-value of 14. Unlike cellulose and other blow-in products, Pour Fill doesn't settle over time. 800/758-7325. www.icynene.com