Avent's Anti-Colic Bottle Nipple's valve integrated in the nipple is designed to keep air away from your baby's tummy to reduce colic and discomfort. As your baby feeds, the valve flexes to allow air into the bottle to prevent vacuum build up and vents it towards the back of the bottle. It keeps air away from baby’s tummy to help reduce colic and discomfort. The nipple shape allows for a secure latch and the ribbed design helps prevents collapse for uninterrupted, comfortable feeding. The anti-colic nipple is made of flavorless, odorless, soft, silicone that resists discoloring and stickiness, a BPA free material. Philips Avent Anti-colic nipples are available in different flow rates, to keep up with your baby’s growth. Recommended to replace nipples every 3 months for hygiene reasons.