CAPCAP

"The original capCAP is one of the most popular water bottle accessories of all time, and it's unique 2-in-1 design has fans all over the world. For the new version, Humangear went back to the drawing board and included some great new features, including a rubberized grips on both caps and a "Cap Keeper" notch on the strap that holds the small cap out of the way when drinking. They have also redesigned the cap-bottle interface so that the capCAP is now compatible with popular stainless steel water bottles from HydroFlask, KleanKanteen, and others."