How to define Insulators

An insulator or dielectric could be conveniently defined as a material that does not conduct electricity, if not the fact all known materials conduct a measurable amount of electricity. Nevertheless, insulators are readily distinguished from conductors. At room temperature, the conductivity of a good insulator typically is more than 20 orders of magnitude smaller than that of a good conductor and the difference becomes larger at lower temperatures.
The physics that underlies the vast difference between the electrical conductivity of insulators and conductors is the first topic considered. The above things that discusses are devoted to properties of insulators, including the importance of the insulator-electrode contacts in determining conduction processes. This article concludes with a brief description of some of the ways an insulator loses its ability to insulate when electrically stressed to the point of breakdown.