Dr. Brown's Natural Flow baby bottles feature a patented internal vent system that helps reduce colic, spit-up, burping and gas. As the baby feeds, air is channeled from the nipple collar through the vent system, bypassing the breast milk or formula, to the back of the bottle. Air never mixes with the breast milk or formula, which minimizes oxidation and helps maintain essential nutrients like vitamins C, A and E. All parts are dishwasher safe. BPA Free. 4oz - single bottle