Cavity wall insulation works by filling the air gap between interior and external walls using a polymer foam that is made from a special plastic that traps air. The foam serves as a substitute for the air gap between the walls.
Houses and buildings with cavity walls use trapped air for insulation. The air gap between the interior and exterior walls prevents the interior wall from becoming moist. It also makes the home colder by transferring heat via convection, which is the process of transferring heat in liquids and gases. Liquids and gases contain particles that bump with substances that have a high temperature. The particles move to an area with a substance that has a low temperature, and they transfer heat upon colliding with the colder material.
Cavity wall insulation uses a foam that replaces the air to prevent heat transfer. The polymer foam and the trapped air are excellent insulators, thus resulting in poor conduction.
Other types of insulation that use trapped air include loft insulation, pipe insulation, hot water tanks and double glazing. Some polymer materials that contain trapped air include bubble wrap and polystyrene foam, which are both ideal materials for packaging due to their low density. Disposable cups used in hot drink machines are also made from polystyrene foam.