Philips Avent Natural Response Bottle Teat - 2 x Baby Bottle Flow 3 Teats for Newborn Babies, 1+ Months, BPA Free Anti-colic valve: The baby bottle is designed to keep air away from the baby's tummy during feeding?Works like the breast: The teat releases milk when baby actively drinks, this is different from the traditional free-flow teats. As with breastfeeding, it can take time for a baby to get used to this.?Natural Response nipple: The unique Philips Avent bottle nipple opening only releases milk when the baby actively drinks.?Right nipple flow: Find your baby's perfect flow rate and personalise your Avent bottle?No-drip nipple: The bottle-feeding nipple only opens to release milk when the baby is feeding.