The thermo mug 420 ml is made of stainless steel. Double walls with vacuum insulation allow to keep the temperature of the contents for a long while (up to 4 hours). Robust leackproof design: 100% leackage protection. Easy to use: open it with a push of the button. The wide mouth makes it easy to wash and pour liquids. Convenient to use in a car. Do not wash in a dishwasher.