Radiant Barriers and Reflective Insulation

Standard insulation—such as batts, boardstock, and spray foam—functions primarily by slowing down two out of the three modes of heat transfer: conduction and convection. Radiant barriers and reflective insulation function by reducing the third type: radiation. This can work, but there is a great deal of misinformation about these systems.

Heat radiates from all objects by way of electromagnetic waves, with the net result being that hotter objects, like the sun, warm up cooler ones. Reflective and low-emissivity materials like aluminum foil can be used as a radiant barrier to control either heat gain or heat loss. A key feature is that they must face an air space to work because radiation moves through space. A radiant barrier sandwiched between two solid surfaces will merely conduct heat.