A dielectric is an insulator that separates the two plates or sheets of the conductor on the capacitor. Isolators are materials that cannot conduct the electric current, for example, plastic, glass, paper, or wood. The dielectric function is to increase the capacitance so that the capacitor can store more electric charge and the electric potential energy.
A capacitor can function if both conductor plates do not touch each other so that the electric charge does not move from one conductor to another. Likewise, so that the electric charge does not move from the conductor to the air, the space between the two conductors must be a vacuum. In the topic about the parallel plate, the capacitor has been discussed the capacitance of parallel plate capacitors which are separated by a vacuum. The capacitance of the capacitor in a vacuum has limitations so that to enlarge the capacitance, placed dielectric between the two plates.