SplashPro's patent-pending design helps keep water from spilling out your wide-mouth bottle when you're trying to take a sip. Compatible with 32 and 40 ounce Hydro Flasks and similar bottles like Iron Flasks, Takeyas, and ThermoFlasks. SplashPro fits snugly into place and won't fall into your bottle. Hydro Flask caps can be screwed into place without pushing the SplashPro into the bottle.