AFAIK Glass is insulator, it doesn't have free electron. It's said metal is a good conductor of heat because it has free electron, glass doesn't have free electron, why it is a good conductor of heat?
There are at least two mechanism of thermal conductivity - free electrons and thermal phonons. The first mechanism can be prevalent in metals, the second one is important in dielectrics. I did not look up thermal conductivity of glass, but such excellent dielectric as diamond has higher thermal conductivity than any metal, as far as I know.