What are the differences between good and bad conductors of heat?

Good conductors of heat, such as metals like copper and aluminum, have high thermal conductivity due to their free electrons that can easily transfer heat energy. Bad conductors, or insulators, like wood or rubber, have low thermal conductivity as they lack free electrons and impede the flow of heat energy. The molecular structure of good conductors allows for efficient heat transfer through collisions between free electrons and atoms, while bad conductors have a structure that inhibits the flow of heat energy.