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Magnet wire is a copper or aluminum wire covered with thin insulation. It is used in the construction of transformers, inductors, motors and electromagnets; among other applications. However, it is not magnetic itself.
The wire itself is most often fully annealed, electrolytically refined copper. Aluminum magnet wire is sometimes used for large transformers and motors. However, because of its lower electrical conductivity, an aluminum wire must have 1.6 times the cross sectional area as a copper wire to achieve comparable DC resistance. Smaller diameter magnet wire usually has a round cross section. Thicker magnet wire is often square or rectangular (with rounded corners) to permit more efficient use of available winding space. Older insulation materials consisted of cotton, paper or silk and were useful for lower temperature applications (up to 105°C). Modern magnet wire typically uses one to three layers of polymer film insulation, often of two different compositions, to provide a tough, continious insulating layer. Magnet wire insulating films use (in order of increasing temperature range) polyurethane, polyamide, polyester, polyeseter-polyimide, polyamide-polyimide (or amide-imide), and polyimide. Polyimide insulated magnet wire is capable of operation at up to 250°C. The insulation of thicer square or rectangular magnet wire is often augmented by wrapping it with a high-temperature polyimide or fiberglass tape, and completed windings are often vacuum impregnated with an insulating varnish to improve insulation strength and long-term reliability of the winding.
In the audio sector, a wire of silver construction and various other insulators such as cotton and Teflon can be found.
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