If you pump directly into these bags, you will never have an accurate measurement of what you pumped. It will always look like the output is greater than it really is. I opened the bottoms fully, and still it always looked like more than was actually in the bag. On top of this, these bags do not freeze flat, so they take up more space in the freezer. After I used the set I bought, I moved to Lansinoh and never looked back.See full review