Before the large-scale use of fossil fuels, removable textile layers kept homes warm in winter and cool in summer.

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.

Modern insulation methods involve the permanent addition of non-structural materials with high thermal resistance, such as fiberglass, cellulose, or mineral wool, to the building surfaces. Viewed in a historical context, this approach is unusual and stems from a shift in architectural style. 2 Preindustrial buildings often didn’t require extra insulation because they had a significant amount of thermal mass, which acts as a buffer to outside temperature fluctuations. Additionally, the building materials themselves could have high thermal resistance.