These silicon teats mimic the shape of the breast enabling baby to feed naturally with the feel of natural nursing. WHAT YOU NEED TO KNOW: Fitted with a system to ensure air stays inside the bottle rather then being taken into baby's stomach, minimising the risk of swallowing air which can lead to painful colic.5 different designs for each use: Size 1: 1 hole, suitable from birth. Size 2: 2 holes, from 1 month. Size 3: 3 holes, medium flow, from 3 months. Size 4: slit with variable flow, from 3 months variable flow. Size 5: 4 holes, variable flow, from 6 months.