The cup is cool and beautiful. Inside is metal, the instructions say it's stainless steel. Made on the principle of a magnetic stirrer, we had those in the laboratory. 😁 . Due to the fact that the magnet is in a plastic case, I wouldn't risk pouring boiling water in there. 🤗 . But mixing cocoa in warm milk or sugar in a cool compote would be very convenient. The product arrived very quickly. I recommend the seller. 😉 👍