i cant figure this out. i hope someone here can. heres the scenario: the dishwasher was run the night before, and my sister emptied it at around 10 am. there are 2 sizes of the particular cups we are talking about here. she thinks she had stacked 2 big ones together, but there was a chance it was a big one on bottom and a small one on top. here are pics showing the cups and how they stack: 2 big cups: small cup on a large cup: sorry about the sizes but i want to retain as much detail as possible in both cases the cups cannot be stacked so that it is airtight. the top glass rest lightly on the bottom, my sister did not jam them together the cups were sitting in the cupboard for about 4 hours. i was sitting in the basement, and my sister was in the living room next to the kitchen, and my mother was upstairs sleeping. i heard a pop/shatter noise, but when there was no uproar upstairs, i figured it was nothing. my sister says she never heard the noise. anyway, about an hour later, i went upstairs for a drink, opened the cupboard and saw the upper glass int he stack had totally exploded. the collected shards: single shard: (sorry my camera wouldnt focus) it was in tiny pices, most in the bottom cup which was unharmed, but the explosion was enough that every single cup in the cupbourd had some tiny pieces of glass inside. there were no huge temperature changes today. does anyone have any idea what happened? if more info is needed, just ask. thanks.