Bests & Worsts Reviews from Amazon

This is a very clever idea. The physics is sound, but there is something wrong with the implementation and it's grossly overpriced. It is based on the physics principle of "phase change" in which huge amounts of energy (joules, hence the name "joulies") are absorbed or released at the two phase change points: melting (change from solid to liquid) and vaporizing (change from liquid to gas). For example, it takes 1 calorie of energy to raise the temperature of 1 gram of water 1°C. But at the melting point, where the water changes from ice to water, it requires 80 calories. It takes 80 times as much energy to melt the ice as to raise it 1°C. That energy is absorbed from the environment and "stored" in the water. This is why salt is added to the ice in old-fashioned ice cream makers. The salt lowers the melting point of the ice causing it to melt. This is why fresh water bodies freeze much more easily than salt water bodies. Anyway, the melting ice absorbs 80 times as much energy as it would by just by raising its temperature. This is called the "heat of fusion". That energy is absorbed from the liquid in the ice cream container causing it to freeze and making ice cream. Without the salt, the ice would melt much more slowly, which would make it take much longer to make ice cream. And we don't want to have to wait for our ice cream. This is what the Joulies are trying to take advantage of. They don't use ice, because the melting point is too low. They chose a type of wax that has a melting point of 140°F (60°C). These materials are called Phase Change Materials (PCMs). And they are used to store and release energy at higher melting points. There is an excellent Wikipedia article on PCMs at en.wikipedia.org/wiki/Phase_Change_Material, if you care to read about them. When the Joulies are cooler than 140°F, the wax inside is "frozen" (solid). If they are placed in a liquid (tea, I hate coffee) that is hotter than 140°F, the wax melts. As it melts, it absorbs a lot of energy from the tea cooling it down. The Joulies website does not say what the heat of fusion number is. Whatever it is, that energy is "stored" in the wax material. Since the tea is in an environment (room temperature) that is cooler than 140°F, it will eventually cool to below 140°F. When that happens, the wax starts to freeze. As it freezes, it releases some of that stored energy, raising the temperature of the tea. All of this magic happens at around 140°F. It's an elegant principle. Sadly, it doesn't work in practice. Well, the physics works, of course, but the effect is so small that is it not worth the price or the inconvenience of having a bunch of noisy little rocks in my thermos. I won't return them, but I doubt that I'll use them much. I'll keep them as a novelty. Maybe I can use them in science experiments with the grandkids - assuming that they even work well enough for that. I imagine that the people submitting the positive reviews are not getting nearly as much of an effect as they think they are. I don't doubt that their drink might stay hot "for hours", but how long does it stay hot without the Joulies? I have a thermos that will keep my tea at a fairly reasonable temperature for at least 2-3 hours without any Joulies at all. With the Joulies, it probably stays hot somewhat longer. I just don't think the effect is that large. The price is shocking! $10 for each joulie? I wonder if these guys are trying to get rich quick. And they already made over $300K on Kickstarter. Another reviewer said that these guys have another Kickstarter project going as well. He may be right that they may be running some kind of game. If I get some time, I'll run a controlled experiment with accurate timings. The only way to be sure is to try and create two environments that are as identical as possible except for the Joulies. I think I might have to find some rocks that are about the same size. I'd start with a fixed volume of water at a fixed starting temperature. Then take a reading every 5 minutes. Maybe I can find a digital temperature probe for my iPhone that will record continuous readings. I'll post the results if I ever get around to it. My advice, get a good thermos. What I'd really like is to find a company to make a digitally controlled, heated thermos. I've tried several so-called "cup warmers". They don't work either. Their problem is that they are trying to keep a volume of liquid in an un-insulated container warm, by heating the rim of the bottom. Because the heating element is exposed, they can't get warm enough to do any good without the risk of burning the user. I believe that the tea in a well-insulated thermos could be kept at a constant temperature with very little energy. I think it could be supplied over the USB port, but certainly by a 12V current.