What is the insulation in a capacitor called?

The insulation in a capacitor is termed a dielectric. A dielectric is a material that does not conduct electricity and is used to separate the conductive plates of the capacitor. Its primary function is to increase the capacitor's ability to store electric charge, allowing it to have a higher capacitance. The dielectric material can influence the performance and efficiency of a capacitor, as it affects how much charge the capacitor can hold at a given voltage.

In capacitors, the choice of dielectric material can vary widely, and common examples include air, paper, ceramic, and various plastics. The effectiveness of a dielectric is measured by its dielectric constant, which is a measure of how much electric field is reduced within the material compared to a vacuum.

The other options refer to different concepts. An insulator is a general term for materials that prevent the flow of electric current, but it does not specifically denote the material used in capacitors. A conductor is a material that allows electricity to flow freely and is opposite in function to a dielectric. Bipolar refers to a type of capacitor that can be charged in either direction, rather than designating the insulating material itself.