316 Stainless Medical Grade Steel,Insulated Water Bottle greatly outperforms 18/8 food grade stainless steel in anti-oxidation and corrosion resistance, it will never leave a metal taste or rust. Avoid the taste of the liquids to change (like tea, coffee and juice).Long Time for Holding Temperature ----Featured dual walls, premium coated copper on the exterior of the inner wall. High performance temperature retention.