I used about 800 Lansinoh bags to freeze breast milk. I wanted to make sure I had enough to last until my 2nd baby was 1 with going back to work. While I made this happen, I am very dissappointed in these bags. At least half of them leak. Doesn't matter which way they were frozen (standing up or laying down) and doesn't matter how we defrost them (in the fridge, on the counter, or in warm water.) At least half of them leak. I did not overfill them and they were treated like gold in their own freezer. If anyone finds a milk bag that doesn't leak, LET ME KNOW as I have another on the way!