Insulation, inhibiting or limiting the conduction of electricity or heat through the use of specific materials. An electric current or voltage is contained by materials (insulators) that offer a high resistance to current flow, will withstand high voltages without breaking down, and will not deteriorate with age. The mechanical properties desired vary with the application: Cables require flexible coatings, such as polyvinyl chloride, while glass or porcelain is used for rigid mountings, such as the insulators used to support power cables. In thermal insulation, there is a reduction of transfer of heat from a hot area to a cold. Thermal insulation is used to keep something hot, to keep something cold, or maintain something at a roughly steady temperature. Heat is transferred through conduction, convection, and radiation. The vacuum bottle thus uses 3 techniques to reduce heat transfers: a vacuum between the walls to combat conduction and convection; silvered walls to minimize the transmission of radiant heat from one wall and maximize its reflection from the other; and supports for the inner bottle made of cork, a poor thermal conductor.