Electrical insulators have no free electrons (or very few), so charge cannot flow through them. This makes them useful for coating wires, covering plugs and handles, and preventing short circuits.
Insulators can hold a static charge on their surface because the charge cannot move away. This is why rubbing insulators (e.g. polythene, acetate) with a cloth produces static electricity.
Common insulators: plastic, rubber, glass, wood, air (when dry).
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