30 oz Stainless Steel Tumbler - 2 Pack Double Wall Vacuum Insulated Tumbler These Tumblers make a perfect Travel Mug, made out of 304 food-grade stainless steel (also known as 18/8), double wall vacuum-insulated to keep your drinks hot or cold, and with a splash-proof closable lid. They have proven to hold coffee hot for several hours and also they can keep ice cubes frozen all afternoon.