 The hot plate, called the "sole plate", is made of aluminium or stainless steel polished to be as smooth as possible; it is sometimes coated with a low-friction heat-resistant plastic to reduce friction below that of the metal plate.The heating element is controlled by a thermostat that switches the current on and off to maintain the selected temperature.The invention of the resistively heated electric iron is credited to Henry W. Seeley of New York City in 1882.