For your peace of mind & their advanced comfort. Colic in infants may be caused by a combination of influences including ingesting air during feeding. The new advanced comfort range from closer to nature is specially designed to help reduce air bubbles in the milk & to encourage a good latch-on to help reduce the risk of baby ingesting air during feeding. The air vents down through the tube & into the air-space at the base of the bottle, completely bypassing the milk. Features Unique tube & value system to provide optimum vending during feeding Unique, easy-latch-on teat shape that promotes continuous feeding Soft, natural-feel silicone teat to make it easier to switch between breast & bottle Easy-hold bottle with slow-flow teat Bottle compatible only with Closer to Nature advanced comfort Teats (not Closer to Nature Easi-Vent Teats) BPA-free