The Pigeon Flexible Slim Neck Nipple (S), has a round-cut hole suitable for Newborns that have not yet developed any jaw muscles. The perfect choice for a seamless transition between breast and bottle feeding. Backed by over 60 years of research on baby's natural suckling motion, our Flexible Slim Neck Nipple is so soft it flexes to the movements of babies' mouth and bends naturally to baby's mouth movement. The nursing bottle's Air Ventilation System (AVSTM) reduces intake of gas, a potential cause of colic. BPA/BPS Free.