Dr Brown's options glass wide-neck bottle is the market's first convertible bottle that can be used with or without the vent system. it is now available in a glass version that some parents prefer. the 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. brown's. 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 options bottles are bpa free.