The Natural Response Nipple works with your baby's natural feeding rhythm, making it easy to combine breast feeding and bottle feeding. The nipple has a unique opening which only releases milk when the baby actively drinks. So when baby pauses to swallow and breathe, the milk pauses too so you can confidently avoid milk loss whether at home or on the go. The wide, soft and flexible nipple is designed to mimic the shape and feel of a breast, helping baby to latch on and feed comfortably. The anti-colic valve is designed to keep air away from baby's tummy during feeding, to help reduce colic and discomfort. Every baby feeds differently, and develops at their own pace. Philips Avent have designed a range of flow rates (0m+, 1m+, 3m+, 6m+ & 9m+), so you can find the perfect one for your baby and personalize your bottle. All of the Natural Response Nipples are made of soft silicone. A wide bottle neck makes filling and cleaning easy along with only a few parts for quick and simple assembly. The ergonomic bottle is easy to grip at any angle to give maximum comfort during feeding, easy for your hands and tiny hands to hold. The Philips Avent Natural bottles and nipples are made of BPA-free material.