Another special version is the VDR resistor i.e. (Voltage Dependable Resistor).
It is made of sintered silicium carbide, a material with the property that its resistance changes according to the voltage applied seeing that its resistance decreased when the voltage is increased.
In popular terms it is used to give a “soft start” to a circuit as its resistance is large right from the voltage starting at zero and decreasing as the voaltage increases. The function almost
corresponds to a check valve with damped opening.