Designed by a doctor in 1996 and patented in 1997, dr. brown’s natural flow® is the only baby bottle to feature an internal vent system that helps to maintain vitamins c, a, & e by minimizing oxidation of breast milk or formula; provides positive-pressure vacuum-free feeding similar to breastfeeding and helps reduce colic, spit-up, burping and gas by eliminating negative pressure and air bubbles. dr.brown’s natural flow® baby bottles are bpa-free and contain no pvc, lead or phthalates and have received numerous design awards.