Simply the best baby bottle. Reduces colic, spit-up, burping & gas. Less oxidation helps maintain vitamins C, A & E + lipids. Patented internal vent system. BPA free. Free of bisphenol-A. Helps maintain vitamins C A & E + lipids. Vacuum-free feeding like breastfeeding. Reduces colic, spit-up, burping & gas. New research. A recent university study set out to measure nutrient levels in baby bottle breastmilk and formula. It was determined that Dr. Brown's fully-vented bottles help maintain levels of important nutrients. The Dr. Brown's vent system reduces air bubble oxidation of the milk, which is very fragile and susceptible to nutrient loss. Patented internal vent system. 1. Air enters the bottle collar and routes directly through the internal vent system. 2. The air channels through the vent tube, bypassing the milk, to the end of the bottle. 3. The vent prevents aeration of the milk, vacuum pressure, and nipple collapse. 4. Baby feeds comfortably while the milk flows freely, like breastfeeding. Contents: 1 - 4 oz/120 ml standard baby bottle; 1 - level-one silicone nipple; 1 - two-piece patented internal vent; 1 - cleaning brush; instructions. Made in the USA.