Locks Milk In, Keeps Air Out: The Teat Stays Full Of Milk, Even When The Bottle Is Horizontal, So Your Baby Can Drink In A More Natural, Upright Position.Designed For Less Air Intake: Unique Airfree Vent Draws Air Away From The Teat, So Your Baby Swallows Less Air As They Drink.Reduces Colic And Fussing*: A Valve In The Teat Prevents Vacuum Build-Up As Your Baby Drinks, Allowing Uninterrupted Feeding.The Airfreetm Vent Can Be Easily Assembled With Any Philips Avent Anti-Colic And Classic+ Bottle. Also Cleaning Is A Breeze, Thanks To The Bottle'S Wide-Neck, And There Only Being A Few Parts To Clean.