WFS Hydro Flask Wide Mouth Sport Cap Flip and Sip. Hydration on the go got easier with the leakproof, insulated Flex Straw Cap. Add it to your favorite Wide Mouth Hydro Flask bottle to easily enjoy cool hydration anywhere. Leakproof when closed Straw is easy to trim to fit your favorite Hydro Flask Flex Strap is easy to transport and comfortable to carry Insulated for maximum temperature retention Removable components for easy cleaning BPA-Free Dishwasher safe Not intended for use with hot liquids