Some of the worst conductors of electricity include rubber, polymer and plastic. A bad electrical conductor is an object or material that does not allow electricity to flow freely through it. An insulator does not allow electric current to pass through it. Most metals, such as copper, are good conductors, whereas most other non-metal materials are bad conductors, or insulators.
Because a portion of the insulator can become electrically conductive if enough voltage is applied, there is no such thing as a perfect insulator. Where it requires much less electricity to get a much higher charge on conductors, it takes a lot of electricity to get a small charge on insulators. This property, known as the breakdown voltage of insulators, essentially makes them poor conductors. Insulators are commonly seen on plugs and cables. The outermost layer of most wires is made of an insulator, such as rubber or plastic. This insulator surrounds the conductor, which is usually some form of copper wire. Not only does this prevent the wire from easily breaking, it also prevents electrical shock.
Many power lines utilize ceramic insulators. Silicone rubber and reinforced plastic are some modern composite insulators. These types of insulators are cheap, light and excellent in polluted areas. However, they do not have the lifespan of glass and porcelain insulators.