[XBob]

a barrier blocks physical passage of something, eg, an aluminum wall is a barrier, but it is not an insulator, which blocks conduction of something less physical - eg heat, electricity etc. For example, the first electron to come out of the wall aluminum wall is not the first electron to go in, it is the last electron in the string of electrons which is bumped, and the first to go out.

[Physicist]

In an electrical insulator, the electrons are not free to move throughout the material. If "electrons" are physical but "electricity" is not, then instead of thinking of a brick wall stopping "cars", think of a brick wall stopping "traffic".

As for thermal insulators and conductors, they are totally different things from electrical insulators and conductors. They work according to different physical principles. A diamond is a lousy electrical conductor, but there is no better thermal conductor.