Question

Conduction of heat takes place through solids where the molecules are closely packed.Then why does a rubber or a glass have low conductivity of heat and are among the best insulators? They are also solids. They also have molecules which are closely packed?

Answer 1

First, let me explain why metals generally conduct heat better than other solids do. In metals, some of the electrons (often one per atom) are not stuck to individual atoms but flow freely among the atoms. Of course, that's why metals are such good conductors of electricity. Now if one end of a bar is hot, and the other is cold, the electrons on the hot end have a little more thermal energy- random jiggling- than the ones on the cold end. So as the electrons wander around, they carry energy from the hot end to the cold end, which is another way of saying they conduct heat.


why rubber is an insulator?

well its because of the space between the molecules which makes it a very bad insulator. its like having a hole in the blanket you sleep in.
Its electrons are locally bound and not free as is the case with metals.
Since there are no free electrons to move the heat from one place to another, hence it is a poor conductor of heat or an insulator.