The term "thermal insulation" refers to a material or combination of materials that slows the transfer of heat from high temperature (hot) regions to low temperature (cold) regions. Thermal insulation is placed between regions or surfaces having different temperatures to reduce heat flux—heat flow rate per unit area. In general, the heat flow increases as the temperature difference increases. The heat flux also depends on the type of material between the hot and cold surfaces. If the material between the surfaces is a thermal insulation—a material with relatively low values of a property called apparent thermal conductivity—then the heat flux will be small. As an added bonus, most building thermal insulation also function as effective sound or acoustical insulation.

The development of better thermal insulation is important since space heating and cooling account for the majority of energy consumption in the residential...