A wax motor is a linear actuator device that converts thermal energy into mechanical energy by exploiting the phase-change behaviour of waxes. During melting, wax typically expands in volume by 5–20%.

Paraffin wax is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to melt above approximately 37 °C (99 °F), and its boiling point is above 370 °C (698 °F). Common applications for paraffin wax include lubrication, electrical insulation, and candles; dyed paraffin wax can be made into crayons. It is not to be confused with kerosene and other petroleum products that are sometimes called paraffin.