Bolometers use the temperature dependency of the electric resistance. The sensitive element consists of a resistor, which changes when it absorbs heat. The change in resistance leads to a changed signal voltage. The material should have a high temperature factor of the electrical resistance in order to work with high Sensitivity and high specific detectivity. Bolometers which work at room temperature use the temperature coefficient of metallic resistors (e.g. black layer and thin layer bolometer) as well as of semiconductor resistors (e.g. thermistor bolometers).