I have a lot of the Pyrex bowls in various sizes. If you keep the lids on, they can be stacked. I've never broken one, but they don't strike me as particularly non-fragile. Sturdier than Mason jars for sure, about the same weight as a glass measuring cup. I don't know if the lids are supposed to be microwaveable or not, but they will distort when heated, so we use the flat silicone lids to heat those too.
I *have* broken a Corningware bowl, but that was by dropping it on a tile floor. I think a tennis ball would have shattered. Hate hate hate tile.

