Size:2 Pack Product Description The Three Flow Nipples are the perfect choice because they feature a unique valve that allows mom to choose between three different flow rates by simply orienting the nipple to the desired flow number. They are made of soft silicone and feature a natural shape which feels more like a mother's breast. This natural shape and feel promotes healthy, active feeding and makes the transition between breastfeeding and bottle feeding easier. They also feature soft nubs on the surface of the nipple which help soothe baby's tender gums during teething. In addition, the Three Flow Nipples feature 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, thus reducing gas and the chances of colic. From the Manufacturer Nuby Feeding nipples fits standard neck bottles (2 pack). Three flow - adjustable for slow, medium and fast flow rates. Anti-colic air system prevents ingestion of air by baby. Teething nubs massage and stimulate gums.