Parents love the Dr. Brown's 4 oz. Bottles 6-Pack - Pink because the patented internal vent system helps reduce feeding problems like colic, spit-up, burping and gas. The system works unlike any other bottle design and fully vents the bottle for vacuum-free feeding, which is similar to breastfeeding. Air never mixes with the breast milk or formula, which helps preserve essential nutrients like vitamins C, A and E and lipids. The award-winning bottles are BPA free and contain no PVC, lead or phthalates.