Zojirushi's stainless steel vacuum insulation mug will keep your beverages hot or cold for hours. The compact design takes minimal space while maximizing capacity. Each flip lid is tightly fitted for excellent heat retention and features a safety lock to prevent accidental opening. Durable and sanitary these mugs have an 18/8 stainless steel interior with Slick Steel finish. Slick Steel is created utilizing electro polishing technology, these products are non-coated on the inside and instead use an electrically charged polishing process to treat and finish the interior. The results is a corrosion resistant surface that repels foreign substances and stains, creating a smooth and ultra clean stainless steel environment for your drinks.