The NaturalFit Advanced Feeding System is engineered to be responsive to the changing feeding styles of babies. Three distinct nipple shapes adapt to the specific needs of growing babies as the natural suck-swallow action develops. The Stage 1 nipple with its unique angle and wide, rounded base fulfills specific needs of the newborn. The angle of the nipple encourages proper positioning and neck support of baby for feeding. This angle also keeps the nipple full of milk, helping to reduce the chance of baby swallowing air. Unique angled nipple with wider, rounded base for proper neck positioning; Twin anti-colic valves help prevent air ingestion, gas and spit-up; Flexors at the base of the nipple enhance elasticity; Internal ridges prevent nipple collapse; Soft, flexible nipple mimics mother?s breast; Soft silicone is easy for baby to latch onto; BPA Free; Clinically Test; Designed for babies 0 months+;.