Vacuum Insulated Technology: Sunwill coffee mugs are with double-walled vacuum insulation technology, keeping your favorite beverages hot for 3+ hours and cold for 9+ hours. Powder Coated Premium 18/8 Stainless Steel: The insulated coffee mug is made from premium 304 food Grade stainless steel, never rust, lead-free, easy to wash, and unbreakable. Each cup is powder coated for a durable finish, with no scratching, peeling, or fading.