Glass isn't that good a conductor of heat. Take a 6" by 1/4" bar of glass and put the end in a gas flame you'll be able hold it by the other end more or less for ever. Now try it with a metal bar of same dimensions...
Glass 1 W/mK, Copper 400 W/mK, Ali 250W/mK, Brass 100 W/mk, Iron 80 W/mK (approx).