The important properties required for the primary cathode material in a solid electrolytic capacitor is the ability to impregnate small pores, high conductivity, low cost, and the most restrictive requirement is the ability to form a non-conductive plug to ‘heal’ leakage sites in the dielectric. Joule heating at a leakage site converts the primary cathode material to a non-conductive material. For example, the MnO₂ is converted to Mn₂O₃ at a temperature of about 500°C. Conductivity is another critical property of the primary cathode material. The difference of conductivity between the conductive polymers and the MnO₂ was the primary reason for introducing this material in tantalum capacitors as a method to obtain lower ESRs.