It's too bad I didn't know how impossible it would be to get the lids off before I had stored a week's worth of milk on these. Neither my husband or I could get the tops off... even using screwdrivers and various other tools to try to pry them off. The only one that came open was the one that dropped on the tile floor as I pulled it out of the freezer, of course, it only came open because the container cracked and the milk cube went flying across the kitchen floor... our dog loved his treat!