Created by a physician, dr brown's natural flow is the only baby bottle with a patented internal vent system that actually helps promote good health in babies. The dr brown's special edition bottle features a patented two-piece internal vent system that works unlike any other bottle design. The vent system fully vents our bottle for vacuum-free feeding, which we call positive-pressure flow, similar to breastfeeding. As the baby feeds, air is channeled from the nipple collar through the vent system, bypassing the breastmilk or formula, to the back of the bottle. Air never mixes with the breastmilk or formula which minimizes oxidation and helps maintain essential nutrients like vitamins c, a and e. Helps maintain vitamins c, a & e - patented internal vent system is proven to minimize oxidation of breastmilk and formula, to help maintain essential nutrients. Positive-pressure feeding - fully vented bottle design provides vacuum-free feeding similar to breastfeeding. Helps reduce colic - vent system eliminates negative pressure and air bubbles to help reduce colic, spit-up, burping and gas.