Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A DC electric current is passed through the junction, which creates a temperature difference by transferring heat from one side of the device to the other. This can be used to cool or heat an object, depending on which side of the device is used. The most common application of thermoelectric cooling is in refrigerators and freezers, where it is used to maintain a constant temperature.