Glass is good insulator because of the following reason:
It is poor conductor of heat and electricity
It doesn't allow the flow of current/electron between two atoms, ions or species.
It can be easily prepared in industries.
It is eco friendly, It does not lead to deforestation like wooden insulator does, and doesn't harm/pollute the environment like rubber and plastic insulator does.
It can be used upto high temperature level because it have high melting point (1700°C)
