Drinking hot beverages can be a tricky business. If you don't want them becoming tepid too quickly, you have to pour them into your mug while they're still too hot. Even then, you're left with a relatively short period in which they're "just right." The designers of the Temperfect mug, however, want to change that. They claim that their mug can keep your drink at the perfect sipping temperature for hours at a time, without using any electricity.
The 16-ounce (473-ml) stainless steel travel mug is a variation on the standard double-wall vacuum flask. In those, insulation is provided by a gap of empty space (from which almost all of the air has been evacuated), between the vessel's exterior and interior surfaces. The tripled-walled Temperfect likewise has a layer of vacuum insulation between its outer and middle walls, but it also features a layer of phase-change material between its middle and inner walls.
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Phase-change materials change from one state to another (such as from a solid to a liquid) when exposed to heat, absorbing some of that heat and storing it as energy in the process. As they cool, the materials revert to their former state, releasing the stored heat. They're currently used in products ranging from building materials to temperature-regulating clothing to baby blankets.
In the case of the Temperfect, this means that excess heat from freshly-brewed coffee (as an example) will be absorbed in just a couple of minutes, bringing the beverage down to a hot-but-drinkable temperature. As the phase-change material cools and reverts, that heat is released to flow back through the inner wall and into the coffee, maintaining its "just right" temperature of about 140ºF (60ºC).
The mug is being developed by North Carolina State University research assistant Logan Maxwell and engineer Dean Verhoeven, who had previously been working separately on the same basic concept. Verhoeven reportedly found a way around the manufacturing challenges that had stalled other peoples' previous attempts at phase-change mugs.
Much of the secret lies in the choice of phase-change material. While Maxwell can't reveal exactly what it is, he did tell us "It is a waxy material that is totally food safe and non-toxic." In other words, if the inner wall ruptures and the material gets into your coffee, it won't kill you.
Logan and Dean are now raising funds for large-scale production of the Temperfect, on Kickstarter. A pledge of US$40 will get you one, when and if they're ready to go. More information is available in the pitch video below.
If you just can't wait, you might also be interested in buying a pack of Coffee Joulies. They're stainless steel little thingies that contain phase-change material, and they're simply placed in the bottom of an existing mug.