ITW ChronoTherm PTC technology employs a conductive polymer material that allows for high wattage heating in sub-zero temperatures. What makes this possible is ITW's proprietary positive temperature coefficient ink that serves as both the heating element and temperature distribution sensor.
This blended carbon/polymer material exhibits a positive resistance change in response to temperature increases, so the PTC heating material is both a heater and a temperature sensor
Click on the image to see a diagram of PTC .