Thermal insulation is a cornerstone of policies aimed at reducing the high energy consumption for heating and cooling buildings. 1 In many industrialized countries, building energy regulations require new and existing buildings to have insulated walls, floors, and roofs, as well as double- or triple-glazed windows. In cold weather, insulation slows down the heat loss from the interior to the exterior, reducing the energy use of the heating system. In hot weather, insulation delays the transfer of heat from the outside to the inside, thereby reducing the energy consumption of the air conditioning system.