Insulators are commonly used as a flexible coating on electric wire and cable. Since air is an insulator, no other substance is needed to keep power where it should be. High-voltage power lines commonly use just air, since a solid (e.g., plastic) coating would be impractical.
An insulated wire or cable has a voltage rating and a maximum conductor temperature rating.
In microelectronic components such as transistors and integrated circuits (ICs), the silicon material is normally a conductor because of doping, but it can easily be selectively transformed into a good insulator by the application of heat and oxygen. Oxidized silicon is quartz, i.e. silicon dioxide.
Some of the Methods of insulating high voltage systems are ceramic or glass wire holders, gas, vacuum, and simply placing the wires with a large separation, using the air as insulation.