Dr brown's options features an unique internal green vent system continues to create 100% vacuum free feeding, which is clinically proven to help reduce wind related colic. This is what makes 9 out of 10 healthcare professionals recommend dr browns for the relief of wind related colic. As baby becomes more developed the bottle can be used without the green vent system to work more like a conventional, teat-vented bottle. The new dr browns scalloped designed teat allows air to vent through the bottle when the green vent system is not used, ideal for when babys feeding is more developed or parents just want the convenience of a teat vented bottle. Dr. Brown's options replacement kit (8 oz/250 ml)