I have about a zillion (low estimate) of these in my classroom! I have all our craft supplies stored in them on a 4ft shelf--the shelf holds about 32 of these! They're easy enough for my first graders to open, but the tops do not pop off when you don't want them to. My only issue with them is that I noticed that the last ones I bought have slightly different tops than my older ones. They still stack on each other well enough, though. They just look a little different, and I like the uniformity of the tubs on my shelf!