What kinds of radiant barrier materials are available?
There are many types of radiant barrier materials on the market, and more are being developed as radiant barriers become more widely used. Five generic types are most common:
• Single-sided foil (one foil side) with another material backing such as craft paper or polypropylene. Some products are further strengthened by fiber webbing sandwiched between foil and backing. The strength of the backing material is important since unreinforced foil tears very easily.
• Foil-faced roof sheathing materials (decking) that come from the manufacturer with a foil facing adhered to one side of the sheathing.
• Double-sided foil with reinforcement between the foil layers. Reinforcement may be cardboard, craft paper, mylar or fiber webbing.
• Foil-faced insulation. The insulating material may be polyisocyanurate, polyethylene"air-bubble" packing or other materials that impede heat conduction.
• Multilayered foil systems. When fully extended and installed so that the foil layers do not touch, these products also form insulating airspaces.
• Radiant barrier "chips" are also manufactured and sold. This product is slightly different than a conventional sheet-type radiant barrier in that the "chips", which are blown onto the floor of the attic — typically to a depth of 3 or more inches, act as a multi-layer product with many "trapped" air pockets. These air pockets cause this product to function somewhat like traditional, fibrous insulation products. Even though this product may collect dust on its uppermost layer, the remaining layers and air spaces work to significantly reduce heat transfer through the ceiling assembly.
Some of these products may have R-values, which may be claimed only if the product was tested according to Federal Trade Commission regulations for insulation.
Although it is not by definition a radiant barrier, there is a low-emissivity paint available that can be applied directly to the underside of the roof decking.
Which material is best?
While the Florida Solar Energy Center strongly recommends radiant barrier systems in attics, it doesn't endorse any particular brand of radiant barrier material. However, we suggest that you look for a few common-sense characteristics:
• Emissivity (the lower the better)
• Fire rating (Uniform Building Code (UBC) Class I, or National Fire Protection Association (NFPA) Class A, as required by building codes)
• Ease of handling
• Strength of reinforcement
• Width appropriate for installation
• Low cost
