I've been using these storage bags for 3+ months now and haven't had a leak yet. They are a nice thick plastic and hold up great with freezing and thawing. They are clean and durable. I have gone through 3 boxes now and haven't had a issue with a single bag yet. I do recommend these bags.I love that these bags have two seal zip strips, so no leaking before they've frozen in your freezer. These are the only kind I will buy from now on!Excellent quality. I had no problems with these bags. Never had any leaks.I've used these bags and the Medela Pump & Save bags. I HATED the Medela bags. They weren't easy to close and leaked sometimes. The Dr. Browns bags have been great. I've never had an issue with them leaking. I like to freeze the milk flat so they defrost fast. These bags are perfect for that. The Medela bags didn't lay flat like these. After trying both the Medela and Dr. Brown I decided not to try any other brands. Dr. Browns are just awesome!These are great bags for milk storage. They are made of a heavier durable material and the double closure is easy to seal and stays closed unlike some other brands like Medela that leak. I'm very happy with them.Great milk storage bag. Very clean and since it has a double zip loc closure, it stays fresh in the freezer.I highly recommend it!