An electrical contact is an electrical circuit component found in electrical switches, relays and breakers. It is composed of two pieces of electrically conductive metal that pass electrical current or insulate when the gap between them is closed or open. The gap must be an insulating medium of air, vacuum, oil, SF₆ or other electrically insulating fluid. Contacts may be operated by humans in pushbuttons and switches, by mechanical pressure in sensors or machine cams, and electromechanically in relays. Contact materials are usually composed of superior conduction materials such as silver or gold. Cheaper metals may be used to reduce costs for the main contact bump and plated with superior metals. The contact arms are typically spring metals to allow operation motion without breaking.