Speaker 1: Welcome to brain Stuff, a production of iHeart Radio. Hey
Speaker 1: brain Stuff, Lauren Vogelbam Here. When the weather is so
Speaker 1: cold that even your best gloves and socks can't keep
Speaker 1: your digits toasty, those little packets of magic that we
Speaker 1: call disposable handwarmers can bring big relief. Handwarmers are good
Speaker 1: to have an emergency's and they're perfect to tuck inside
Speaker 1: your bittens during winter activities like skiing, ice skating, or
Speaker 1: just on your daily commute. But how exactly do these
Speaker 1: little packets work. They are not filled with tiny demons
Speaker 1: who warm your hands with hell fire, nor is it
Speaker 1: some gamma radiating goo that will turn your paws into
Speaker 1: hulk smash style superhands. The science behind those handwarmers is
Speaker 1: actually pretty simple. It turns out they use the same
Speaker 1: process that transforms iron into rest, just a lot faster.
Speaker 1: There are five main ingredients inside a disposable handwarmer iron powder, water, salt,
Speaker 1: activated charcoal, and some kind of water absorbent material. But
Speaker 1: of course they don't get hot until you open the
Speaker 1: air tight plastic wrappers that the packets come in. That's
Speaker 1: because the final ingredient that makes them work is oxygen
Speaker 1: to become hot. Oxygen from the air flows into the
Speaker 1: packet and reacts with the iron powder, water and salt
Speaker 1: that's already there, which oxidizes the particles of iron, that is,
Speaker 1: it turns them into iron oxides, also known as rust.
Speaker 1: Oxidation is sometimes used as another term for rust, because
Speaker 1: rust is perhaps the most well known version of oxidation,
Speaker 1: but lots of different substances can oxidize anyway. What's happening
Speaker 1: in the packet is that the iron powder is giving
Speaker 1: away electrons to the oxygen that comes in. Water has
Speaker 1: to be present in order to break up molecules of
Speaker 1: oxygen so that the reaction can happen. The water absorbent
Speaker 1: material in the packet hangs onto the water molecules for
Speaker 1: safe keeping until you open the packet. Meanwhile, the salt
Speaker 1: helps the oxidation along because it accelerates the flow of electrons.
Speaker 1: You've probably observed this if you've noticed that exposed metal
Speaker 1: on a car will rest more quickly if the car
Speaker 1: is driven on salt treated roads in the winter, or
Speaker 1: if you've noticed a lot of rust on chains or
Speaker 1: fences that are in or near seawater the versus ones
Speaker 1: that aren't. But okay, the process of rusting is exothermic,
Speaker 1: meaning it gives off heat, But when your car's fender rusts,
Speaker 1: it doesn't feel hot, and that's because that process happens
Speaker 1: very slowly, even when it is accelerated by salt. The
Speaker 1: reaction is greatly sped up in disposable handwarmers, and that's
Speaker 1: where the construction of the packet and the other ingredients
Speaker 1: come in. It may be simple science driving this reaction,
Speaker 1: but control holling it for the precise effect of creating
Speaker 1: a certain amount of warm for a certain period of
Speaker 1: time is complicated. The material of the packet has to
Speaker 1: let in just the right amount of oxygen. They're made
Speaker 1: with microporous materials, meaning they have tiny holes to let
Speaker 1: oxygen in at the gaseous equivalent of a slow drip.
Speaker 1: Warmers for hands have very tiny holes, whereas the warmers
Speaker 1: designed for feet have slightly larger ones. That's because there's
Speaker 1: less air inside your boots and shoes, so those warmers
Speaker 1: need more access to oxygen in order to activate. Then
Speaker 1: you've got that activated charcoal, which serves to distribute the
Speaker 1: heat that's created evenly throughout the packet so that you
Speaker 1: don't wind up with any extra hot clumps. Manufacturers can
Speaker 1: tweak how fast the reaction happens and how long it
Speaker 1: continues producing heat by changing the size of the iron
Speaker 1: powder particles. Smaller particles with more surface area will heat
Speaker 1: up faster, and by increasing the amount of iron in
Speaker 1: the PA could Overall, they're designed to last anywhere from
Speaker 1: a few hours up to a full day. So it's
Speaker 1: not demons and it's not scary chemicals. It's not even magic.
Speaker 1: But the heat in that handwarmer is toasty. Those little
Speaker 1: packets can produce temperatures between a hundred and a hundred
Speaker 1: and eighty degrees fahrenheit. That's eighty two degrees celsius, which
Speaker 1: should keep your digits nice and cozy. And it's totally
Speaker 1: safe throw used disposable handwarmers in the garbage. No has
Speaker 1: Matt team required. Today's episode is based on the article
Speaker 1: how do disposable handwarmers work? On how stuffworks dot com
Speaker 1: written by Kristen Hall Geisler. Brain Stuff is production of
Speaker 1: i Heeart Radio in partnership with how stuffworks dot com,
Speaker 1: and it's produced by Tyler Klang. Four more podcasts my
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