I was a little worried at first about purchasing this flask, I have never used Vevor glass before. It is heavy walled, clear with slight distortion, it has no marking for the type glass used, the only markings are $24/40 and 2000 ml. It has a very heavy center neck, standard size side neck. So, it was go or blow time, with me far away from the soon to be boiling hot acid and unknown or untested by me brand of lab glass. I cranked the heat to maximum.I used this flask under constant maximum heating for 8 hours straight doing this distillation. It worked fine with no problems, it cleaned up well and is ready to be used again when called upon.