Extended cathode foil assures that the capacitor element stays cool. Cornell Dubilier offers three standard constructions of screw-terminal capacitors: potted, rilled and ThermalPak. Potted is the lowest in cost but only modestly improves thermal resistance and cans need to be oriented vent-plug up so that the tar doesn’t block it. A Rilled style has the capacitor element captured by spoon-shaped dimples in the can called rills. It provides superior vibration and shock withstanding. ThermalPak is generally the preferred construction.