Why do some materials conduct and others don't?

Materials conduct electricity based on their atomic structure and the availability of free electrons. Conductors, like metals, have a high density of free electrons that can move easily through the material, allowing electric current to flow. In contrast, insulators, such as rubber or glass, have tightly bound electrons that do not move freely, preventing electrical conduction. The differences in electron mobility and bonding determine a material's ability to conduct electricity.