Most hot drinks are kept warm by insulated cups or thermos bottles. But even those eventually cool down. There's another way, though, and it involves using phase-change materials that are engineered to absorb and release heat at specific temperatures and maintain those temps for hours at a time.
The latest phase-change materials on the scene, called PureTemp, were developed by Entropy Solutions and come in 35 different temperature-regulating states. The company used one of the materials to create innovative coffee mugs that keep beverages at 160 degrees for several hours, double what an insulated thermos can do. Unlike other phase change materials out there, these use vegetable oils as the base chemical and as a result are not toxic or flammable. Not only are they safer, they're biodegradable.
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The PureTemp coffee cup has a coil inside filled with the phase change material. When you pour hot coffee inside, the warm liquid heats the coil. The phase change material melts, absorbing some of the heat energy from the coffee, until the temperature reaches 160 degrees. If the coffee starts to cool below that point, the phase change material in the coil releases the stored heat, bringing the temperature of the coffee back up to 160 degrees. Some heat does escape outside of the cup, but it takes hours. For comparison, a paper coffee cup cools to room temperature in about 40 minutes.