On thermal travel mugs.

So the cafe I work at got these neat stainless steel travel mugs in, and true to form, all us staffers got to take one home. And in the middle of a cold snap a month or two ago, one of my coworkers was telling me how she left her hot coffee out in her Jeep all bloody day, and when she got back, it was still warm!

Amazing! "But I don't get it," she said. "It's steel, and doesn't metal transfer heat pretty quickly?"

Well, that's really only half the story. First off, not all metal transfers heat quickly, but that's a tale for another time. The important part of this equation is that the travel mugs are vacuum-insulated. In fact, most thermal products nowadays are. And the reason why is pretty simple - because vacuums are amongst the best insulations available to us.

Heat is, after all, the agitation of molecules. Picture a bouncy castle with a kid with four cookies and a hot chocolate railing around in it. That kid is going nuts, bouncing off the walls, screaming her lungs out, doing what kids do. She's got a lot of kinetic energy to burn. Now picture the same kid two hours later, passed the fuck out in the middle of the thing or wherever the fuck she landed. She's burned off all her energy, and has none left to do anything but sleep.

This is the difference between a molecule that is hot versus one that's cold. It's a matter of energy. Now, how many kids on a sugar rush do you think you can fit in that bouncy castle? How many will fit if they're all totally zonked out? Suddenly the idea that things expand and contract when they're hot or cold makes sense, no? Things take up less room when they are still.

But I digress. The fact is, thermal energy, like kinetic energy, is transferred through impact. When molecules smash into each other, they transfer the energy of the impact into the next molecule until an equilibrium is established. This is why if you preheat a container before you put a hot liquid in it, it'll keep said liquid hotter longer because the average between those two temperatures is significantly higher than if you had started with a cold container.

Which brings me to the value of the vacuum-insulated container. A cross-section of one of our steel travel mugs would reveal two thin layers of steel separated by an empty space, which, before you so callously cleft the doohickey in twain, contained absolutely nothing. No air, no liquid, nothing.

Think about that. Nothing. In the absence of any molecules to transfer energy to, the tiny bouncy castle kids that make up your double tall bound back from the walls with absolutely zero loss in kinetic energy, meaning your tasty beverage remains just as hot. Is it perfect? No. Obviously, they're still hitting the air at the unsealed top of the mug, so heat is bleeding out that way. And no manmade vacuum is flawless; there's always going to be a teensy amount of air or particulate matter bouncing around in there. But all the same, vacuums make for fantastic insulation because there's simply nothing there to agitate.

Of course, nature abhors a vacuum. Which means when you toss that fucker in the dishwasher or run it over with your car or chuck it at a brick wall because the Eagles lost again, you run the risk of cracking the hull. And when that happens, air rushes in, completely nullifying the mug's insulating properties. No longer do you have a magical heat-maintaining device; you just have a chunk of metal that holds stuff for you. It's also why we don't insulate shit like our walls with vacuums - try to nail one painting into the wall, and you're boned.

So there you go. This is why your fancy thermoses and travel mugs keep hot things hot and cold things cold - it's all about molecular energy transfer. It's also why if you need to keep anything at a stable temperature - soup, hollandaise, melted chocolate - look to your travel mugs.

Cheers, kids. See you next time.