Substances that allow heat energy to flow through them easily are called good conductors of heat or thermal conductors. Some good conductors of heat are copper, aluminium, gold and iron. On the other hand, substances that do not allow heat energy to flow through them easily are called bad conductors of heat or thermal insulators. Glass, mica, cotton, cork, wood, asbestos, plastics and ebonite are some of the bad conductors of heat.