Bornfree glass baby bottles are made to provides mothers with the most advanced, clinically tested baby feeding systems .Born Free Wide Neck Glass Bottles new innovative air vent helps eliminate colic symptoms such as gas and spit-up by reducing the build up of vacuum and is also medically acknowledged to reduce the risk of middle ear infection. The unique inner valve prevents side-leaks, and unlike other vented bottles, allows you to shake freely when mixing.Each bottle comes with a level 1 nipple and a cover The Born Free feeding system is especially suitable for breast fed babies who are being introduced to bottle feeding. The unique air valve begins the steady flow of liquid when a baby starts to nurse - just like with breast feeding.