After trying these bottles for a week, I tossed them all out. My son was continuing to have alot of gas, and was unable to adequately get the formula from the nipples. When I called Playtex, and asked what I could do to make it easier for him to get the formula, I was told that if I used any other nipple than the Vent Air nipple, it would negate the benefits of using this system. The representative also said that newborns have a harder time since they are trying to put the whole top portion of the nipple in their mouth instead of just the tip of the nipple. Since you can't reason with a newborn to try drinking their bottle another way, I gave up.