Electrolytic capacitors are specified where high values of capacitance are required in the least amount of space (high volumetric efficiency). This property is called high CV ratio. They are formed by electrochemical processes in which oxide dielectrics are grown in and on porous aluminum and tantalum foil and pellets. The metal foils are acid etched to make them porous, increasing their effective exposed areas from 6 to 20 times. High CV ratios are made possible by the thin oxide layers formed on the plates of the capacitors. The pellets are also made so that they are porous or spongelike and have large exposed surfaces. However, electrolytic capacitors have higher leakage current than electrostatic capacitors because of the impurities embedded in the foil and the electrolyte. This current increases with temperature while voltage breakdown decreases with temperature. Electrolytic capacitors also have higher power factors than electrostatic capacitors, causing losses called equivalent series resistance (ESR).
