Electrolytic capacitors:

All the above mentioned types of capacitors give relatively small values of capacitance. They are nonpolarized, menas that they can be hooked up in the circuit in any direction. An electrolytic capacitor gives considerably greater capacitance than any above types, but it should be connected in the proper direction in the circuit to work right. Thus, an electrolytic capacitor is the polarized  component.

Electrolytic capacitors are constructed by rolling up aluminum foil strips, separated by the paper saturated with the electrolyte liquid. The electrolyte is a conducting solution. When direct current flows through the component, the aluminum oxidizes due to the electrolyte. The layer of oxide is nonconducting, and forms dielectric for capacitor. The layer is very thin, and this results in the high capacitance per unit volume.

Electrolytic capacitors can posse's values up to thousands of microfarads, and at times units can handle thousands of volts. These capacitors are often seen in the audio frequency circuits and in direct current power supplies.