Both PTC and NTC are thermistors. 
According to the temperature coefficient, it is divided into positive temperature coefficient thermistor (PTC) and negative temperature coefficient thermistor (NTC). The positive temperature coefficient thermistor (PTC) has a higher resistance value at higher temperatures, and the lower the resistance value of the negative temperature coefficient thermistor (NTC) at higher temperatures, they belong to the semiconductor device.
A thermistor is a resistor whose resistance value is extremely sensitive to temperature, also called a semiconductor thermistor. It can be made of single crystal, polycrystalline, and semiconductor materials such as glass and plastic. This resistor has a series of special electrical properties. The most basic characteristic is that its resistance varies greatly with temperature and the volt-ampere curve is nonlinear.
A sensitive component whose resistance changes with temperature. In the operating temperature range, the resistance value increases with temperature and is a positive temperature coefficient (PTC) thermistor; the resistance value decreases with temperature rise is a negative temperature coefficient (NTC) thermistor.
PTC is the abbreviation of Positive Temperature Coefficient, which means a positive temperature coefficient, which refers to a semiconductor material or component with a large positive temperature coefficient. Generally speaking, the PTC refers to a positive temperature coefficient thermistor, abbreviated as a PTC thermistor. A PTC thermistor is a typical temperature-sensitive semiconductor resistor. When a certain temperature (Curie temperature) is exceeded, its resistance increases stepwise with increasing temperature.
NTC (Negative Temperature Coefficient) is a thermistor phenomenon and material with a negative temperature coefficient that decreases exponentially with increasing temperature. The material is a semiconductor ceramic obtained by sufficiently mixing, molding, sintering, or the like using two or more metal oxides of manganese, copper, silicon, cobalt, iron, nickel, zinc, etc., and can be made to have a negative temperature coefficient. (NTC) thermistor.
If someone know about we Mainiko’s heating products, you may find phenomenon when turning on the power in the front 5mins, the red light keeps twinkling during the time. After that, the red light will AUTO turn into white light after the 5mins. Why will this appear? Because we set an NTC chip into all our heating products to achieve the overheating function. Turning the red light to the white light, it decreases the heat to protect people from over-high temp.
Do you think it a safety design? Why not leave your comments as for our design inspiration?