A bimetal snap disc thermostat is disclosed in which a steel disc cup is provided for strength and/or environmental resistant properties. Positioned within the disc cup is a disc seat formed of aluminum. A bimetal snap disc is positioned in the disc seat and operates the thermostat switch through an axially movable bumper. A ring of rubber like foam material is positioned between the body assembly and the disc on the side of the disc remote from the disc seat. The aluminum disc seat reduces temperature calibration drift of the disc during the cycling of the disc which occurs during the use of the thermostat. The foam ring also tends to reduce bouncing and thereby tends to reduce temperature calibration drift. Also the ring functions to insure that the disc remains properly seated in its aluminum disc seat.