How does an insulator stop the flow of an electric current

It is stable and less conductive

Explanation:

The ability of a substance to conduct electricity is based on the electrons in the orbits of its atoms. Insulator have high electrons in their outermost orbit hence making them stable and less conductive thereby stopping the flow of current however we can't fully say it stops the flow of current because when a very high voltage of electric current passes through it, it tends to conduct electricity also.