Perhaps no home insulation seals your house as completely and as thoroughly as the spray-on foam insulation known as Icynene, which is made from castor oil. When contractors spray the substance onto a wall or ceiling it has the thickness of paint. Once it hits the surface, Icynene expands nearly 100 times it volume. The puffy sponge cake-like substance creates a thick blanket of insulation that tightly seals air leaks [source: Cabot]. Not only does Icynene stop drafts, it also muffles noise [source: Cabot]. Icynene has an R-value of R-3.6 per inch of thickness, which can reduce a home's energy bill by 30 to 50 percent [source: Missouri Insulation & Supply].
Icynene works so well because it traps air in tiny bubbles during the foaming process. As the foam cures, the air remains in place. Although it looks like the top of lemon meringue pie, Icynene allows water vapor to escape, which prevents mold from forming [source: Cabot]. However, Icynene has a couple of problems. First, it's expensive -- about three times the cost of fiberglass. Also, since Icynene seals a house so tightly, builders need to install a ventilation system. And in colder climates, that ventilation system will have to include an air exchanger to warm incoming air [source: Cabot].