The Dr. Brown's baby bottle bundle includes their popular anti-colic glass bottles and vent cleaning brushes to keep bottles functioning properly. The 4 oz narrow glass bottles feature an internal vent system clinically proven to reduce colic, spit-up, burping and gas. The vent system provides a vacuum-free feeding experience closest to breastfeeding by allowing air flow into the bottle while preventing the nipple from collapsing. This enables the baby to feed at their own pace. The breast-like nipple shape also encourages a proper latch. By preserving nutrients and aiding digestion, Dr. Brown's bottles help babies sleep better. The bottles grow with your baby and can be used with or without the vent system. The vent cleaning brushes are designed specifically for Dr. Brown's bottles. The small brushes easily maneuver through the vent system to remove blockages and keep components clean. They also fit most other anti-colic and narrow or wide-neck bottles. Lightweight and versatile, these reusable brushes can even be used to clean sippy cups and straw cups. With clinically-proven anti-colic glass bottles that support natural feeding and specially designed vent cleaning brushes, this bundle contains everything you need for safe, comfortable bottle feedings as your baby grows.