Plastic, Wood, Rubber, Paper, Glass
Electrical conductors are materials that conduct electricity; insulators don't. Why? Whether a substance conducts electricity depends on how easily electrons can move through it. Protons don't move because, while they would carry electrical charge, they are bound to other protons and neutrons in atomic nuclei. Valence electrons are like outer planets orbiting a star. They are attracted enough to stay in position, but it doesn't always take a lot of energy to knock them out of place. Metals readily lose and gain electrons, so they rule the list of conductors. Organic molecules are mostly insulators, in part because they are held together by covalent (shared electron) bonds and also because hydrogen bonding helps stabilize many molecules. Most materials are neither good conductors, nor good insulators. They don't readily conduct, but if enough energy is supplied, the electrons will move.
Some materials are insulators in pure form, but will conduct if they are doped with small quantities of another element or if they contain impurities. For example, most ceramics are excellent insulators, but if you dope them, you can get a superconductor. Pure water is an insulator, but dirty water conducts weakly and salt water, with its free-floating ions, conducts well.
10 Electrical Conductors
The best electrical conductor, under conditions of ordinary temperature and pressure, is the metallic element silver. It's not always an ideal choice as a material, though, because of its cost and because it tarnishes. The oxide layer known as tarnish is not conductive. Similarly, rust, verdigris, and other oxide layers reduce conductivity.