Materials that are not good at conducting current are called insulators, and insulators are also called dielectrics. Their resistivity is very high. Definition of insulator: objects that are not easy to conduct electricity are called insulators. There is no absolute boundary between insulator and conductor. Insulators can be converted into conductors under certain conditions. Note here: the reason for conductivity: whether solid or liquid, if there are electrons or ions that can move freely, they can conduct electricity. If there is no free moving charge, under certain conditions, it can produce conductive particles, then it can also become a conductor.

Conductor refers to the material with low resistivity and easy to conduct current. The existence of a large number of free moving charged particles in a conductor is called carriers. Under the action of external electric field, the carrier makes directional movement and forms an obvious current.

Metal is the most common type of conductor. The valence electrons in the outermost layer of a metal atom can easily break away from the bondage of the nucleus and become free electrons, leaving positive ions (atomic reality) to form a regular lattice. The concentration of free electrons in metals is very large, so the conductivity of metal conductors is usually greater than that of other conductor materials. The resistivity of metal conductors generally decreases with the decrease of temperature. At very low temperatures, the resistivity of some metals and alloys will disappear and become "superconductors"