This mug is made of foodgrade 304 stainless steel, liner of coffee mug will not produce any taste and rustfree, and it is durable and not easy to breakOur coffee mug has a vacuum double walled insulation design that ensures beverage can stay either hot or cold over time, letting you enjoy hot or cold drinks. The transparent plastic lid with a rubber gasket, which is well tightness, it is easily swiped to open while keeping away from splashing.