insulator

Insulator is the material or covering which prevents or reduces the transmission of electricity, heat, or sound. All electrical devices are insulated for protection from the passage of electricity. Thermal insulators keep things hot, cold, or maintain an even temperature. Sound insulators act as mufflers. Electrical insulation is the absence of electrical conduction. Electronic band theory (a branch of physics) predicts that a charge will flow whenever there are states available into which the electrons in a material can be excited. This allows them to gain energy and thereby move through the conductor (usually a metal). If no such states are available, the material is an insulator. China is the leading producer of insulators.