We've always found OXO products to have an advantage on just about all the competition, and their water bottles are no exception. OXO has made these bottles both easy to drink from and easy to fill by creating two openings, a narrow one at the top for drinking, and large opening farther down for filling, cleaning and adding ice or supplements. You can see where the larger opening is; the top part of the bottle is darker in color and is threaded to the bottom for easy opening and closing. The drinking opening is protected by a stainless-steel cap that is permanently secured to the bottle by a coated, stainless-steel cable and the bottle itself is made of rugged, BTP-free Tritan. This may be the ultimate water bottle for taking to the gym or into the great outdoors. OXO water bottles have a capacity of 24 ozs. and included measuring markers for monitoring hydration and for adding supplements.