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A composite insulator, also called a dielectric or nonconductor, is a material that resists the flow of electric current. This type of silicone rubber material is used in parts of electrical equipment intended to support or separate electrical conductors without passing current through itself. The term is also used more specifically to refer to insulating supports that attach electric power transmission wires to utility poles or pylons.

Composite insulators are less costly, lighter in weight, and have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas. However, these materials do not yet have the long-term proven service life of glass and porcelain.