From the Manufacturer Created by a physician, Dr. Brown's bottles feature a patented internal vent system that eliminates the vacuum and air bubbles to help reduce colic, spit-up, burping and gas. The positive pressure design allows babies to feed comfortably, because the vent system eliminates the air bubbles and vacuum. Baby feeds comfortably while the milk flows freely, like breastfeeding. Helps maintain vitamins C, A & E plus lipids. Easy to clean, dishwasher safe, BPA free