How much ripple current a capacitor can withstand is proportional to its temperature characteristics. The ability of the capacitor to dissipate heat is determined by its thermal resistance. The temperature rise, shown on this slide as ΔT, is the thermal resistance from the capacitor core to ambient temperature times the power from the ripple current. The thermal resistance is shown by the Greek letter theta, and its units are degrees Celsius per watt. If one watt of power heats the capacitor 5°C, then the thermal resistance is 5°C per watt. The power is the ripple current squared times the load resistance. Current often has the symbol I and the power would be I²R. The R in capacitors is often expressed as ESR, equivalent series resistance. To lower the temperature rise, the thermal resistance can be lowered and the power dissipated can be lowered. And lower temperature means longer capacitor life.