PTC Thermistors (thermal resistor), also called PTC stone, are ideal heating elements. Thanks to self-regulation properties, heating devices based on PTC thermistor technology can generally dispense with control and regulating components as well as with over-temperature protection, PTC thermistor heating elements are used wherever measurement and regulating equipment as well as heating devices must be housed in tight confines. PTC Heating elements can be designed to be square, rectangular, round, ring or doughnut form, or housed in aluminum, stainless steel, silicon casing.