The Medium Flow Dual Surface Nipple provides your baby with the ultimate in comfort and function by combining a soft surface for feeding with a firmer dimpled surface for teething. The top of the nipple is made of soft silicone, and features a medium flow valve that is perfect for milk. The base of the nipple is made of a firm silicone with raised offset surfaces that are great for a teething. In addition, the Medium Flow Dual Surface Nipple features anti-colic vents along the base which help prevent a vacuum from forming in the bottle. This reduces the amount of air the baby ingests, and thus, reduces gas and the chances of colic.