From mountain trails to morning yoga class, our Standard Mouth Insulated Sport Cap lets you hydrate one-handed and on the fly. It’s 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.