The 18-ounce Hydro Flask Wide Mouth features double-wall, vacuum-insulated technology capable of keeping drinks cold for up to 24 hours or hot for up to 6 hours. Constructed from 18/8 stainless steel, the interior is non-porous to prevent bacterial buildup, unwanted odors, and lingering flavors. On the outside, the BPA-free Hydro Flask features a powder-coat finish. It’s compatible with most third-party water filters, as well as Hydro Flask’s Straw Lid accessory.