DR. BROWNS NATURAL FLOW BABY BOTTLES ARE THE ONLY BOTTLES DESIGNED BY A DOCTOR TO HELP REDUCE COLIC, SPIT-UP, BURPING AND GAS. DR. BROWNS BOTTLES FEATURE THE PATENTED INTERNAL VENT SYSTEM, WHICH CREATES POSITIVE-PRESSURE JUST LIKE BREASTFEEDING. THIS FULLY-VENTED BOTTLE DESIGN PRODUCES A MORE COMFORTABLE FEEDING BY ELIMINATING THE VACUUM AND EXCESS AIR INGESTION. IT'S THE VENTING SYSTEM YOUR BABY DESERVES, IN A CHOICE OF BOTTLES TO FIT YOUR LIFESTYLE. DR. BROWNS BOTTLES ARE ALSO EASY TO CLEAN AND DISHWASHER SAFE.