Radiant heat is the type of heat that you feel. A radiant or reflective barrier is a thermal type of insulation that prevents heat transfer via thermal radiation. The barrier material in thermal insulation resists and reflects heat to prevent the transfer of energy through the boundaries of two systems at different temperatures. As heat is always transferred from a higher temperature region to a lower one, a heat barrier will prevent the transfer of radiant heat due to its low emitting/reflective surface. Because the material in radiant barriers reflects radiant heat that has negligible R-values, they can also be classified as thermal insulation.
Radiant barriers are typically installed in residential homes primarily to reduce cooling costs and summer heat in spaces like attics. With attic temperatures exceeding 180 degrees your insulation system is vital to your homes comfort. The highly reflective material in radiant barriers reflect, rather than absorb radiant heat, however, they do not reduce heat conduction the way that thermal insulation material does. They are more effective in hot climates and where cooling air ducts are situated in an attic. Studies show that radiant barriers can reduce cooling costs dramatically by more than 40%. The effectiveness is also matched in the winter time as temperatures dip below freezing.
By a combination of convection, radiation, and conduction, heat travels from a warmer area to a cooler area.
Most radiant barriers consist of highly reflective materials such as aluminum foil covering both sides (or one side) of certain substrate materials including plastic film, cardboard, air infiltration barrier material, or oriented strand board. Some radiant barriers are fiber reinforced to increase ease of handling and durability. They can be combined with other types of insulation materials to form reflective insulation systems. In such combinations, radiant barriers can act as facing material for thermal insulation.
The effectiveness of radiant barriers depends a great deal on proper installation and therefore should ideally be installed by a certified insulation experts who are aware of building and fire codes and how to employ the best safety precautions during and after installation. It is easier to incorporate into a new home but can also be installed in existing structures, especially in open attics.