I purchased the case of 4. One cracked on the second use. No cold shock involved. Simply heating water over flame, as per intended use. I would strongly advise against heating using this flask, since you risk having 5 liters spilling all over your work area. The second issue is less significant, but puzzling. One of the 4 flasks had a neck opening diameter significantly smaller than the others, such that it required a different sized stopper. Very strange to see that level of dis-uniformity in something that I presume comes off an assembly line.