This simple mug has a copper-plated tank exterior with a vacuum between the walls. That means the temperature of your drink has no medium for the heat or cold to transfer through. Your drink will truly stay as hot or cold as science allows. Even filled with ice or boiling water, the bottle will never sweat or get hot to touch! The VIOMI vacuum insulated mug adopts the advanced 316 stainless steel, which has acid-proof and alkali-proof characteristics, and is free of rust. The integrated metal cup body which eliminates redundant decor, gives you the comfortable hand feeling, and resists friction. The lid adopts detachable design, so that you can easily clean the cup thoroughly without leaving a dead corner for your drinking health.