Born free active flow 5oz eco bottle is designed to be used right from birth and can be used up to 18 months with interchangeable born free teats including slow medium amp fast flow the active flow bottles feature a silicone valve that allows milk to flow only when the baby suckles and lets babies control their milk flow according to their needs the built in venting system helps to relieve infant colic and helps your baby learn to wean from breast feeding to bottles