What Is Foilback Insulation?

Foil-Back Insulation

• "Foil-back insulation" is insulation with a highly reflective foil covering. It's also called a "radiant barrier" because the foil -- aluminum foil -- reflects radiant heatwaves back toward their source, effectively keeping them from passing through. Conventional insulations, on the other hand -- fiberglass, cellulose and foam -- absorb heat, merely slowing its movement. Radiated heat is the movement through the air of invisible electromagnetic heat waves from a warm surface to a cooler surface. In summer, up to 93 percent of heat that enters homes is radiant heat; in winter, 65 to 80 percent of heat lost from houses is due to radiant heat loss, according to InsulationStop.com, a reflective foil insulation retail/wholesale website.

How it Works

• Foil insulation works because aluminum foil has properties that allow it to reflect, rather than absorb, most radiant heat that reaches it; yet it emits little radiant heat from its surface when facing open air space. Open space is key: For it to work, there must be open space of at least 3/4 inch surrounding the foil. The open space provides room for radiant heat to reflect away.

Material

• Foil used for insulation is thicker than the kitchen material you're used to; it has backing material such as craft paper or polypropylene to prevent the foil from tearing. Fiber webbing between the foil and the backing adds additional strength in some insulation. Some radiant-barrier insulation is perforated with tiny holes to allow moisture to pass through, but not heat. Perforated insulation is frequently required when insulation is placed on an attic floor. The perforations prevent moisture, due to activities such as showering and washing clothes, from rising during cooler weather from the ceiling below and condensing or freezing and causing water damage to the ceiling and insulation.

Summer and Winter

• In summer, the heat conducted into the attic from the roof and walls is radiated back outward by foil insulation. In winter, heat rises from the bottom of the house into the attic and potentially through the roof. A radiant barrier radiates heat back to the house's interior.

Installing

• Install radiant barriers according to whether keeping the house warm or cool is most important, Attic Foil Radiant Barrier Supply recommends. To save on summer cooling, staple the barrier to the bottom of the attic rafters. In colder areas, where keeping warm is more expensive, install the barrier over existing insulation. In areas receiving a weather mix, the best solution is to also lay the barrier over existing insulation, the supply advises. If the house's ductwork is in the attic, also staple insulation to the bottom of the rafters.