Dr. Brown's Natural FlowÃ‚Â® Options Glass Wide-Neck Bottle features the market's first Convertible Vent System for all stages of your baby's growth and feeding styles Ã¢â€šÂ¬Ã¢â‚¬Å“ plus is now available in a glass version that some parents prefer. We recommend using the Internal Vent System to experience all the health benefits of our bottle. It helps reduce feeding problems, helps digestion and helps preserve vitamins. Some moms and dads find removing the vent a convenient option as their baby's feeding becomes more developed. The nipple venting creates a paced flow, and provides a feeding experience similar to most nipple-vented bottles. Dr. Brown's Options Wide-Neck Glass Bottles are BPA free and feature an ergonomic design that's easy to fill and hold. The silicone nipple has a broader base which some breastfeeding moms prefer. Available in 5 oz/150 ml and 9 oz/270 ml sizes.