the voltage proof of electrolytic capacitors decreases with increasing temperature. for some applications it is important to use a higher temperature range. lowering the voltage applied at a higher temperature maintains safety margins. for some capacitor types therefore the iec standard specifies a "temperature derated voltage" for a higher temperature, the "category voltage u". the category voltage is the maximum dc voltage or peak pulse voltage that may be applied continuously to a capacitor at any temperature within the category temperature range t. the relation between both voltages and temperatures is given in the picture at right.