Review on AOZEX 64 oz Stainless Steel Water Bottle - Half Gallon, Double Wall Vacuum Insulated with 2 Leakproof Lids - Keep Drinks Cold for 24 Hrs/Hot for 12 Hrs! by Brandon Gaines

This cap is stainless steel on the inside, just like my Kleen Kanteen but much easier to unscrew. They fill in cold water or add ice (weird taste, not worth it). Once it's empty I fill it with water from a 40 ounce single wall wedge can that was in the fridge and fill the rest at room temperature. The next day, after adding room-warm water and letting it sit for several hours, the water stays just as cold. We're definitely drinking more water (without conscious effort) since we got that big bottle.