I decided to buy these bottles around 3 months ago after reading up on BPA. When my daughter was first born we had tried Avent, but they leaked. We switched to Dr. Brown's, but decided on the Born Free bottles due to BPA. I did have major issues with nipple collapse with these bottles. It didn't matter what I did, the nipples collapsed. So I read another review from a customer who said she put the Dr. Brown's vent system in these bottles. I tried that and they work PERFECTLY. I have had NO NIPPLE COLLAPSE at all now. The only thing that I do have issues with is if you decide to make a full 9 oz. bottle, they will leak when using the Dr. Brown vents...which is what happened with the Dr. Brown's bottles anyhow. But other than that, these have been the best bottles that I've had and I'm planning now and buying a few more. I highly suggest buying the Dr. Brown's wide-necked vent system to go with these. There are websites where you can actually buy individual parts to bottles.