This is interesting it’s a device called a Coffee Joulies which claims to keep your drink at the perfect temperature for up to five hours. The device which resembles a glass bean is placed inside the thermos with the hot drink. It absorbs the extra thermal energy in the drink when it is hot and then releases this energy to keep the drink at an optimum drinking temperature as it starts to cool down. The beans are made of a non toxic material sealed within the stainless steel shell. They only work, however, when the drink is insulated with a lid. It’s an interesting idea, but I do wonder whether they are any more effective than an ordinary thermos.