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How hand warmers work: It's all science

Monday, February 3rd 2020, 11:47 am - Yes, we seriously got this in-depth about hand warmers, you're welcome.

It’s a simple chemical reaction creating heat and keeping you on the ski hills longer. We're talking about hand warmers!

Here is everything you need to know about the tiny hot packs.

What are hand warmers made of?

  • Iron Powder
  • Water
  • Salt
  • Activated Charcoal
  • Vermiculite

How does a hand warmer work?

“There is an intricate chemical process that takes place inside these bags,” says Orbax, who is the Science Communication & Media Officer with the University of Guelph. “The process is oxidation, basically rusting.”

As soon as oxygen hits these packs, the process begins. That’s why when you purchase them they are sealed.

“This product is microporus, which means there are a bunch of tiny tiny holes. This allows the oxygen to seep in and activate what is inside,” explains Orbax.

Once the oxygen gets to work the ingredients inside essentially create rust and that rust gives off heat.

What does the inside of a hand warmer look like?

You should not try this at home! However, we wanted to dissect the insides in a safe lab with an expert.

At first glance, it looks like a pile of dirt! To recap, the pile of “dirt” is iron powder, salt, activated charcoal, vermiculite and water.

UGC: By Rachel Schoutsen, hand warmersTo recap the pile of “dirt” is iron powder, salt, activated charcoal, vermiculite and water. Courtesy: Rachel Schoutsen

So what happens when you cut open a hand warmer?

There are no sparks or crazy obvious chemical reactions but the surface that the concoction is on slowly becomes warm. We spilled it onto a white paper and we also noticed the paper absorbing some of the water that is within the solution. Orbax was able to point out some very small “whiteish” flecks which he said were vermiculite.

How long will a hand warmer create heat?

Some vary by brand, but usually about 8-10 hours. At best up to 15-16 hours.

Why does a hand warmer stop working?

“Hand warmers stop generating heat for the simple reason that they run out! Once all the iron powder has rusted, or more likely, once all the water and salt have been used up in the oxidizing process, the hand warmers simply stop generating heat and eventually cool down”, explains Orbax.

When and where were hand warmers invented?

The first hand warmer was invented in 1923 by a man named Niichi Matoba in Japan. He has the patent for the oxidation process that produces heat.

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