How do radiant barriers “block” heat transfer?
Aluminum foil the operative material in attic radiant barriers – has two physical properties of interest here. First, it reflects thermal radiation very well. Second, it emits (gives off) very little heat. In other words, aluminum is a good heat reflector and a bad heat radiator. Your grandmother probably made use of these properties through “kitchen physics.” She covered the Thanksgiving turkey with a loose “tent” of aluminum foil before she put it in the oven. The foil reflected the oven’s thermal radiation, so the meat cooked as evenly on top as on the bottom. She removed the foil briefly to let the skin brown, but when she took the bird from the oven, she “tented” it with foil again. Since aluminum doesn’t emit much heat, the turkey stayed hot until the rest of the meal was ready. Cooking a turkey is a simple analogy, but the same principles of physics apply to an attic radiant barrier. Aluminum foil across the attic airspace reflects heat radiated by the roof. Even if the radiant
