The Tommee Tippee Closer to NatureŽ Anti-Colic Feeding Bottles with Slow Flow Nipples are intuitively designed for babies with excessive spit-up, fussiness and gas. This bottle is designed especially for babies with extra sensitive tummies. the super-sensitive anti-colic vent tube provides optimum venting during feeding to help reduce colic and discomfort that together with the slow flow non-vented nipples that are designed to prevent air and vacuum build up. The nipple mimics natural feel, flex and movement of breastfeeding and allows for an easy and natural transition between breast and bottle. This bottle is also heat sensitive and will warn you if the temperature of the milk is too hot by turning red, or if its the appropriate temperature, it turns blue.