Dr Brown's Wide Neck Milk Bottles, 120ml (2-Pack)Dr Brown's Wide Neck Milk Bottles, 120ml (2 Pack) Dr. Browns bottle features a patented two piece internal vent system that works unlike any other bottle design. The vent system fully vents our bottle for vacuum free feeding, which we call positive pressure flow, similar to breastfeeding. As the baby feeds, air is channeled from the teat collar through the vent system, bypassing the breastmilk or formula, to the back of the bottle. Air never mixes