How a radiant barrier works
Radiant barriers work on principle of reduction of heat loss due to thermal radiation. All materials give off, or emit, energy by thermal radiation and the amount of energy emitted depends on the surface temperature. In homes, this heat loss generally occurs between the roof deck and the attic floor. During day time solar energy is absorbed by the roof, heating the roof and causing the underside of the roof sheathing and the roof framing to radiate heat toward the attic floor. Radiant barriers is placed on the attic floor and it reflects most of the heat radiated from the hot roof back toward the roof making upper surface of insulation cooler than it would have been without a radiant barrier. This minimizes the heat transfer to the room below the ceiling. A radiant barrier also reduces heat losses through the ceiling in winters. Thus a radiant barrier effectively reduces heat transfer from within and outside of building.