I had been using other bottles for a while, and my baby did okay with them. He would take 3-4 ounces, but it seemed like a struggle for him and he was constantly moving the nipple around in his mouth. On a whim, I decided to try these, and they are amazing! He can take 6 ounces no problem, and seems much happier doing it. He immediately relaxes when we use these bottles, and he never did that with the other bottles.See full review