I started out making espresso into double-walled borosilicate cups and switching to porcelain was such a game-changer (it took me at least 3 years to figure this out). The double-walled cups do an amazing job at insulating the espresso, but if I'm pulling a shot I want to just drink it. Most shots are usually too hot for my taste right out of the machine, and I'd either burn myself, sit there blowing on the damn thing for too long, or the taste would be sub-optimal due to the temp being too high. You can come across Lavazza porcelain cups pretty easily and these are perfect for single shots; I use some slightly wider porcelain ones someone got me from some local shop called Starbocks (or something similar to that I think) for double shots. Any reason you are set on glass besides looks? You'd be hard-pressed to find many cafes in Italy serving espresso in anything other than porcelain. I think they've nailed it.