Substance that blocks or retards the flow of electric current or heat. An insulator is a poor conductor because it has a high resistance to such flow. Electrical insulators are commonly used to hold conductors in place, separating them from one another and from surrounding structures to form a barrier between energized parts of an electric circuit and confine the flow of current to wires or other conducting paths. Electrical insulators include rubber, plastic, porcelain, and mica. Thermal insulators. which break up the heat-flow path by absorbing radiant heat, include fiberglass, cork, and rock wool.

This entry comes from Encyclopædia Britannica Concise.
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