General-type glow plug
In the general-type glow plugs, the resistance value of the heat-generation coil is not changed by the temperature, and a constant current runs.

Rapidly heating glow plug
For the rapidly heating glow plug, a heat-generating coil in which the resistance becomes equal to the temperature increase is used. Since, immediately after power distribution, the resistance is small and a large current runs, the temperature of the plug rises more rapidly than that of general-type glow plugs, but, when resistance becomes high, a small current runs, which curbs the temperature rise.

QGS-type glow plug (one material)
The QGS-type glow plug is used in combination with the special QGS controller. The resistance of the one-material-type QGS glow plug is small and a very large current runs through the heat-generating coil, in comparison with general-type and rapidly-heating glow plugs. Therefore, the temperature rises rapidly. This helps to reduce preheating time considerably and to improve starting performance.