Designed to reduce colic, gas and reflux ; Locks milk in, keeps air out, for easy upright feeding: The teat stays full of milk, even when the bottle is horizontal, so your baby can drink in a more natural, upright position. This can help reduce reflux, aid digestion, and make feeding time more comfortable for you and your little one.- Teat stays full of milk, not air: Our unique AirFree™ vent draws air away from the teat, so your baby swallows less air as they drink. This can help reduce common feeding issues such as colic, reflux and gas.- The AirFree™ vent can be easily assembled with any Philips Avent Anti-colic and Classic+ bottle. Also as the vent is one single piece, cleaning is a breeze.