insulator

An insulator is a material that does not let charge flow, which makes it the protective counterpart to a conductor. Rubber, glass, plastic, dry wood, air and ceramic all insulate, and that is why one of them wraps every wire, forms the handle of every electrician's tool and separates the contacts inside a switch.

Insulating is not the same as conducting poorly by accident. A semiconductor such as silicon sits in a third class of its own, allowing charge through only under certain conditions, and that is the class electronics is built on. A true insulator simply stops the flow.

Safety questions turn on the pair. The current is carried inside the conductor and kept off the hand by the insulator around it. Damage that insulation, wet it, or overheat the wire, and the insulation fails — which is what a short circuit and an overloaded cable both really amount to.