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. The positive pressure design allows babies to feed comfortably, because the vent system eliminates the air bubbles and vacuum. All parts are dishwasher safe. Vent Reservoirs are exclusive for the Standard 8-ounce Dr. Brown"s Natural Flow baby bottles. They are meant to replace worn or lost vent reservoirs. These vent reservoirs are an integral part of the Dr. Brown"s patented internal venting system.