Dr. Brown s Natural Flow Preemie Flow Nipple is the slowest flow sized just right for premature babies newborns or babies experiencing feeding difficulties. Preemie Flow Nipple together with Dr. Brown s Anti-Colic internal vent system is clinically proven to reduce colic. Dr. Brown s bottle and nipple provide a more comfortable feeding experience for baby by decreasing spit-up burping and gas. This vacuum-free feeding is closest to breastfeeding and Dr. Brown s Preemie Flow Nipples provide a consistent flow so baby can feed at their own pace. The breast-like nipple shape encourages a proper latch for a more natural bottle feeding experience and eases the transition from breast to bottle and back again. The Preemie Flow Nipple and Anti-Colic vent system is proven to help preserve bottle milk nutrients and aid in digestion for a better night s sleep. Made of super-soft 100% silicone the Preemie Flow Nipple fits all Dr. Brown s narrow bottles. Safe for use in dishwasher (top rack only) electric and microwave sterilizers or boiling water. BPA free.