I have been using these bags for the last several months of exclusive pumping. I fill it up to 6 oz and have never had any leaks. However they are nowhere near accurate when measuring. I measure 6 oz in a bottle and then pour it in, zip it 3/4 of the way, squeeze out the air, and zip it the rest of the way. They stand up well, freeze perfectly, and defrost very quickly. Sometimes when baby needs a bottle NOW, but I only have cold milk from the fridge, I'll pour it into a bag and warm it up, which cuts the warm up time drastically.
Rating: [5 of 5 Stars!]