Hydro Flask Standard Mouth Insulated Sport Ca pis a replacement sport bottle cap for all Hydro Flask Standard Mouth bottles.From mountain trails to morning yoga class, our Standard Mouth Insulated Sport Cap lets you hydrate one-handed and on the fly. Its the first insulated sport cap specifically designed to keep water in your Hydro Flask bottle ice cold, sip after sip. Compatible with all Standard Mouth bottles Insulated for enhanced temperature protection Quiet, “no whistle” valve BPA-Free and Phthalate-Free Sport Cap is not intended for use with hot liquids and is not leakproof Fits (click below links): Hydro Flask Standard Mouth Insulated Bottle (18oz) Hydro Flask Standard Mouth Insulated Bottle (21oz) Hydro Flask Standard Mouth Insulated Bottle w Sport Cap (21oz) Hydro Flask Standard Mouth Insulated Bottle (24oz)