How do you insulate a wire?

Answer 1

Cover it with a nonconducting material.

In the early days of electrical wiring materials like cotton cloth, natural rubber, and gutta percha were used.

Now wires are almost always insulated with plastics (e.g. PVC, nylon, Teflon).

Answer 2

Wire can be insulated with any material that does not conduct electricity.

One of the most common insulators is plastic, most electrical wires these days are coated with plastic.

Ceramic is also used in industry to insulate wire cable.