Do radiant barriers work? Short answer, yes they do work.
First, tests by the Florida Solar Energy Center (FSEC) and other groups show that they work. Second, manufacturers are improving the quality of radiant barrier materials. Third, many decking manufacturers are producing roof decking products with a radiant barrier preinstalled, saving money on installation costs in new housing and redecking applications.
A radiant barrier is a layer of aluminum placed in an airspace to block radiant heat transfer between a heat-radiating surface (such as a hot roof) and a heat-absorbing surface (such as conventional attic insulation). In hot climates, benefits of attic radiant barriers include both dollar savings and increased comfort. Without a radiant barrier, your roof radiates solar-generated heat to the insulation below it. The insulation absorbs the heat and gradually transfers it to the material it touches, principally, the ceiling. This heat transfer makes your air conditioner run longer and consume more electricity. In summer, when your roof gets very hot, a radiant barrier cuts air-conditioning costs by blocking a sizable portion of the downward heat gain into the building. An aluminum foil radiant barrier blocks 95 percent of the heat radiated down by the roof so it can't reach the insulation.