Insulator

Once the materials are separated, they retain their charge because electrons cannot move freely through an insulator. The charge is therefore described as static.

The charge remains where it builds up most readily on an insulator, such as a plastic rod or rubber balloon, because charge cannot move easily through it. On a conductor such as metal, charge moves easily and will usually flow away through your hand if you hold it while rubbing it. An isolated conductor can nevertheless retain charge: the metal dome of a Van de Graaff generator is supported by an insulator.