The Cool Roof Rating Council explains it like this: If you want to stay cool on a hot day, it's better to wear a white T-shirt than a black one because it reflects rather than absorbs heat. A cool roof is like that white T-shirt: It reflects heat from the sun and stays cooler, thus transferring less heat into the building.
In the past, the roofing materials themselves needed to be light-colored for this concept to work. But new treatments allow consumers to choose darker materials that will reflect heat back into the atmosphere, as well.
Without question, these materials cost more than traditional roofing. Eco Home Magazine cited one estimate at $80 per square foot more. Of course, experts argue that a lower electric bill in the blazing days of August will help you recoup those costs quickly.