Dr. Brown’s Natural Flow Baby Bottles feature an innovative, fully-vented design that enhances baby’s feeding experience while reducing feeding problems. With a patented 2-piece internal vent system that creates positive-pressure flow, Dr. Brown’s bottles eliminate air bubbles in formula or milk and help to reduce colic, spit-up, burping and gas. This system is also proven to help preserve bottle milk nutrients, including vitamins C, A, and E, which are critical for infant health. By creating a vacuum-free, fully vented bottle, Dr. Brown’s offers baby an easy digestion feeding experience that is closer to breastfeeding than any other bottle. The patented vent system and silicone nipple also work together to create a controlled flow so babies nurse at their own pace. Dr. Brown's bottles are BPA, PVC, lead and phthalate free for your baby's safety. Each bottle comes with 1 Level-One silicone nipple, 1 two-piece patented internal vent system, 1 cleaning brush and instructions.