How Do Disposable Hand Warmers Work?

little packets work. They are not filled with tiny demons who warm your hands with hell fire, nor is it some gamma radiating goo that will turn your paws into hulk smash style superhands. The science behind those handwarmers is actually pretty simple. It turns out they use the same process that transforms iron into rest, just a lot faster. There are five main ingredients inside a disposable handwarmer iron powder, water, salt,

activated charcoal, and some kind of water absorbent material. But of course they don't get hot until you open the air tight plastic wrappers that the packets come in. That's because the final ingredient that makes them work is oxygen to become hot. Oxygen from the air flows into the packet and reacts with the iron powder, water and salt that's already there, which oxidizes the particles of iron, that is, it turns them into iron oxides, also known as rust.

Oxidation is sometimes used as another term for rust, because rust is perhaps the most well known version of oxidation, but lots of different substances can oxidize anyway. What's happening in the packet is that the iron powder is giving away electrons to the oxygen that comes in. Water has to be present in order to break up molecules of oxygen so that the reaction can happen. The water absorbent material in the packet hangs onto the water molecules for

safe keeping until you open the packet. Meanwhile, the salt helps the oxidation along because it accelerates the flow of electrons. You've probably observed this if you've noticed that exposed metal on a car will rest more quickly if the car is driven on salt treated roads in the winter, or if you've noticed a lot of rust on chains or fences that are in or near seawater the versus ones

that aren't. But okay, the process of rusting is exothermic, meaning it gives off heat, But when your car's fender rusts, it doesn't feel hot, and that's because that process happens very slowly, even when it is accelerated by salt. The reaction is greatly sped up in disposable handwarmers, and that's where the construction of the packet and the other ingredients

come in. It may be simple science driving this reaction, but control holling it for the precise effect of creating a certain amount of warm for a certain period of time is complicated. The material of the packet has to let in just the right amount of oxygen. They're made with microporous materials, meaning they have tiny holes to let oxygen in at the gaseous equivalent of a slow drip. Warmers for hands have very tiny holes, whereas the warmers

designed for feet have slightly larger ones. That's because there's less air inside your boots and shoes, so those warmers need more access to oxygen in order to activate. Then you've got that activated charcoal, which serves to distribute the heat that's created evenly throughout the packet so that you don't wind up with any extra hot clumps. Manufacturers can tweak how fast the reaction happens and how long it continues producing heat by changing the size of the iron

powder particles. Smaller particles with more surface area will heat up faster, and by increasing the amount of iron in the PA could Overall, they're designed to last anywhere from a few hours up to a full day. So it's not demons and it's not scary chemicals. It's not even magic. But the heat in that handwarmer is toasty. Those little packets can produce temperatures between a hundred and a hundred and eighty degrees fahrenheit. That's eighty two degrees celsius, which

should keep your digits nice and cozy. And it's totally safe throw used disposable handwarmers in the garbage. No has Matt team required. Today's episode is based on the article how do disposable handwarmers work? On how stuffworks dot com written by Kristen Hall Geisler. Brain Stuff is production of i Heeart Radio in partnership with how stuffworks dot com,

and it's produced by Tyler Klang. Four more podcasts my Heart Radio, visit the heart Radio app, Apple podcasts or wherever you listen to your favorite shows,