A radiant barrier is a highly reflective, low emissivity foil, used as a type of insulation system to permanently reduce energy costs.  Radiant barriers are ‘technically’ not an insulation material, due to the fact they are only a thin sheet of reinforced aluminum foil, however with an air space of approximately 3/4″ or more, radiant barriers have a theoretical R-value of 53. Radiant barriers affect radiant (radiation or Electromagnetic) heat transfer, the single most efficient type of heat transfer, by reflecting that radiation away from the radiant barrier. A typical home will loose heat in the winter and gain heat in the summer and the majority of that heat is radiant heat, so stopping radiant heat transfer in both the winter and summer months is the most effective way to reduce energy cost.