Tommee Tippee Closer To Nature 2x Med Flow Teats the new nipple was designed in collaboration with breastfeeding experts, mimics the natural flex, movement and softness of a mum's breast, to make switching between breast and bottle easier than ever before.The nipple encourages your baby's natural feeding process so that switching between breast and bottle becomes natural. With its unique Easi-vent anti-colic valve (which you can actually see working) the Closer to Nature Easi-vent teat is at the heart of an entire breastfeeding support system.