The Airfree Vent Is Designed To Help Your Baby Swallow Less Air. The Teat Stays Full Of Milk, Even When Horizontal, For Upright Feeding. Reducing The Air A Baby Ingests Can Help Ease Common Feeding Issues Like Colic, Gas And Reflux.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.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.Clinical Studies Have Shown That The Philips Avent Bottle Reduces Colic And Fussing*. How? A Valve In The Teat Prevents Vacuum Build-Up As Your Baby Drinks, Allowing Uniterupted Feeding. This Can Help Reduce Colic, Gas, Spit-Up And Burping.