Works like breast¹: the teat releases milk when baby actively drinks, which is different from the traditional free-flow teats; as with breastfeeding, it can take time for baby to get used to this This baby bottle is made of premium quality borosilicate glass, a BPA-free, heat and thermal shock resistant material; it can be safely stored in the fridge or warmed, it's easy to wash and sterilise The unique Natural Response teat opening only releases milk when the baby actively drinks, when pausing to swallow and breathe, no milk flows; the no-drip teat design prevents spills and lost milk Right teat flow: find your baby's perfect flow rate and personalise your Avent bottle; age is a guide, but your baby's approach will help determine when to move to a higher or lower teat flow rate Anti-colic valve for your and your baby's well-being: it keeps air away from your baby's tummy during feeding to reduce colic and discomfort Easy to clean: the wide bottleneck makes filling and cleaning effortless; only a few parts for quick and simple assembly The set includes: 1x 4oz Natural Response glass baby bottle with slow flow teat (Flow 2)