Philips Avent Natural fast flow nipples are designed to help babies combine breast and bottle feeding. The nipple’s wide shape is similar to the shape of a breast, and its soft, rounded nipple encourages natural latch on. A unique petal design increases flexibility and helps prevent nipple collapse while your baby feeds. Also, the advanced, twin anti-colic valves keep air in the bottle and out of babies’ tummies, making feeding more comfortable. The nipples are made of soft, durable silicone.