Capacitors have a dielectric component and, like any other insulator, it is not perfect. Because it is not perfect, a small amount of current will leak through that insulator and this is what is referred to as the leakage current. This leakage current designation is most important in power supply circuits and in amplifier coupling circuits. Aluminum capacitors are well known to have high leakage currents and are usually not used for storage applications or for use in coupling because of this. Additionally, the leakage current in an aluminum capacitor will increase as the temperature of the device increases.