This 2-pack Dr. Brown's bottle bundle includes their designer Anti-Colic Options wide-neck 9oz baby bottles with Level 1 nipples for 0m babies, plus Level 3 medium-fast flow wide-neck nipples for 6m babies. The Anti-Colic Options bottles feature an internal vent system clinically proven to reduce colic by decreasing spit-up, burping and gas. The vacuum-free feeding experience provides a consistent flow rate closest to breastfeeding, so baby can feed at their own pace. These bottles also help preserve nutrients and aid digestion. The Level 1 nipple is designed for newborns, with a slow flow rate and breast-like shape to encourage proper latching. As baby grows, the Level 3 nipple allows a medium-fast flow rate for 6m babies transitioning to self-feeding. Both BPA-free silicone nipples easily fit onto all Dr. Brown's wide-neck bottles. With the adjustable internal vent, Options bottles grow with your baby from newborn through toddler. Combined with the 2 different flow rate nipples, this bundle offers a complete feeding system tailored to your baby's developing needs.