Let’s say you love to be outside, but hate to be cold. What do you do? Learn how to make DIY hand warmers, of course!

Perhaps you’ve toted a pack of commercial hand warmers along to a football game or crammed them into the toe of your ski boots. But did you ever think about how to make DIY hand warmers? While there are various types of commercial hand warmers, this version uses rusty iron filings. With salt, iron, and water, you can create a instant pocket-portable heat source! These homemade instant hand warmers don’t need a microwave or sewing machine. Instead, you’ll learn how to make DIY hand warmers the easy way—with science.

What You Need:

What You Do:

  1. Put 30 grams (approximately 1 1/2 tablespoons) iron filings in 3×5 zip-top bag. how to make DIY hand warmers - mix chemicals
  2. Add 1 1/2 tablespoons salt.
  3. Add 1 1/2 tablespoons sodium polyacrylate.
  4. Finish with 1 1/2 tablespoons of warm – NOT hot – water.
  5. Carefully remove air and zip bag closed.
  6. Place 3×5 bag inside 4×6 bag. Carefully remove air and zip bag closed.
  7. Shake, squeeze, and knead the mixture for 30 seconds or so until a slush forms inside the smaller bag and the water is completely mixed in. Be cautious to set the bag down if it gets too hot.

What Happened:

To truly understand how to make DIY hand warmers, you need a basic grasp on chemical reactions first. So what is a  chemical reaction? It’s when a substance (like iron or salt) is altered in some way, also know as a chemical change. This occurs in various ways: Two or more chemicals can combine into one, two chemical compounds turn into two different chemical compounds, or one chemical compound separates into two or more chemicals.how to make DIY hand warmers

For your homemade hand warmers, you introduced the iron filings to salt, air, and water, which produced iron oxide, or rust. This chemical is considered an exothermic reaction. Exo means out and thermal means heat, so an exothermic reaction is literally one in which heat (or light) is released. In this case, while the oxidation is occurring, heat is produced. The sodium polyacrylate, or water gel powder, helps lock in moisture so the chemical reaction can take place. But once the air-activated process is complete, no more heat will be emitted—this can take from one to several hours!

Safety note: To avoid tetanus exposure, throw away hand warmers when you’re finished experimenting.

Further exploration:

How does the reaction change if you add more iron filings? How does it change if you add less? What about the other ingredients? How does adjusting the ratio of salt or water gel powder affect the reaction? Repeat the experiment using varying amounts of materials and record your results. Use a lab thermometer to record the temperature of each experiment. Use a stopwatch to time how long the bag stays heated.

Download the printable instructions for how to make DIY handwarmers.