How can insulators be characterized?

Insulators can be characterized as substances with tightly bound electrons. This property means that the electrons in insulator materials do not move freely, which prevents the conduction of electricity. In contrast to conductors, where electrons can move freely to produce an electric current, insulators have electrons that are closely associated with their atomic nuclei, leading to their ability to resist electric flow. This tightly bound electron structure is what makes insulators essential in preventing unwanted electrical currents and ensuring safety in electrical applications.

In the context of the other options, materials that allow free movement of electrons describe conductors, while substances that conduct heat well and materials with high thermal conductivity denote characteristics associated with good thermal conductors, which do not fit the definition of insulators.