I have 6 Brilliance containers of various sizes.   One day I noticed a big crack on the bottom of the medium container..  I don't know what caused it.  I never used the medium container in the microwave.  I have a small container that's getting a spider web like crack on the side.  I've used this one in the microwave a few times.   It took some time getting used to the snug lids, but then this is why they are leak proof.   My family loved these containers, but we're disappointed that they are getting cracks.