This is created by a physician. Dr. Brown's Natural Flow baby bottles feature a patented internal vent system that helps reduce colic, spit up, burping and gas. Its positive pressure design allows babies to feed comfortably, because the vent system eliminates the air bubbles and vacuum. All the parts are dishwasher safe. Dr. Brown's 3-pack of wide neck 8 oz Polypropolene baby bottles comes with Level 1 silicone nipples and 1 cleaning brush.