The extra soft, naturally shaped AVENT nipple makes it easier to switch between breast and bottle feeding, and promotes healthy, active feeding. The built-in valve flexes with babys natural feeding rhythm and lets baby control the flow of milk, which can help reduce the risk of overeating and spit-up. The valve also prevents a vacuum from forming in the bottle to keep air out of babys tummy. This reduces colic and gas after feeding.The Newborn Flow Rate is most like breastfeeding flow, making these nipples ideal for newborns or breastfed babies of all ages.