The Physiological Teat has been designed and tested in co-operation with authoritative specialists to simulate as much as possible the physiology of the mother''s breast during feeding. The special Anti-Colic Valve allows air to flow in the feeding bottle thus favoring the steady flow of milk and avoiding the formation of vacuum in the bottle. This allows the baby to suck the milk steadily without swallowing air. Regular Flow is for 0 months babies Medium Flow is for the babies from 2 to 4 months Adjustable Flow is from 2 months and above Fast Flow for babies from 4 months and aboveMeasurment:Length: 14.17Width: 5.91Height: 17.91