Evaporative cooling bandanas really work

Originally published at: http://boingboing.net/2017/07/18/evaporative-cooling-bandanas-r.html

I love that these gel things are available in bandannas. I have been using the same (or very similar) tech to keep my insulin cool in hot weather - it’s a pack from Frio and it works wonderfully well with re-soaking every 2 days to 2 weeks depending on the weather. These evaporative cooling gel balls are great - I hope to keep finding them in other products.

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Did anyone else think: This is Boing Boing. It’s not “bandanas” it’s “bananas”.


I keep having a very hard time when I look at the headline now. Thanks!


I have one that I bought years ago. It works quite well.

The gel crystals have been in common use for years now – in diapers. The same crystals that soak up water and slowly let it evaporate also soak up other substances in your Huggies or Depends (although you probably shouldn’t leave them on long enough to let that evaporate).

The same gel goes into another product with which I am impressed: StormTek storm bags. Basically, flat pack sandbags that are activated by soaking in water until they plump like hot dogs.


A water-absorbent crystal gel? I think that’s what you get with Lapis and Sapphire fuse.


Probably polyacrylamide. Not truly crystalline, but it’s a porous polymer network with lots of water-attracty groups (-C(O)NH2) on the sides of the crosslinked polymer chain, so it can reversibly expand and contract as water fills and leaves the spaces between the chains. Also used in contact lenses and for gel electrophoresis, the technique to separate and analyze mixtures of proteins.

Decent video of the swelling gel “crystals”:


Diapers are polyacrylate rather than polyacrylamide. Might be that, too. Might be a copolmer of both.


Just look at it!


I saw a demo of the crystals (not sure of the chemical geometry) at the Astronaut Training Experience in Florida. The presenter had a beaker with about an inch of the crystals in the bottom, then filled it with water (tinted yellow, for effect) and flung it out towards the audience. In the second or two between pouring in the water and throwing, the crystals had absorbed all the water and swelled to the point where they didn’t dislodge from the container. A NASA product.


These take about 10-15 minutes to absorb the water. A quick dousing does not work.

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NASA: helping you urinate safely in your work attire since 1961.


There are probably several variants on the crystals, depending on intended use. The storm bags do take about 15 minutes to fully inflate; OTOH, you don’t want your Pampers to take that long unless you are okay with your kid finger painting with the contents.

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They’ve existed since at least the mid-90s. This post brought to mind a memory of my father - he owned an auto-repair shop in Oklahoma and we used these things in the summer to keep cool. There was always an old coffee pot carafe in the refrigerator with a few of these soaking, next to the Gatorade.

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In my youth, my family crossed the Nevada desert in a VW bus without air conditioning. We quickly learned that if you soak beach towels in water and close them in the top of the front doors, covering the open windows, and draping down inside onto the arm rests, you can plant your elbow onto the lower part of the towel on the arm rest and lock it into place. Then when you travel at highway speed, the entire van is cooled down dramatically as the dry wind billows through the soaking towel.

They had none of the gel beads, so you had to soak them after half an hour again. You needed a few gallons of water with you.


That was Tang!


There are a lot of do-it-yourself videos and instructables. The Amazon price is low enough that I wouldn’t bother. But … how about one with a 4th Doctor scarf pattern? That would be cool!

My work here is done.


Before auto a.c. become common, there were evaporative cooling devices that mounted in a car window.

In hot weather, I just wet a bandana and wear it on my head.

Similar devices are available to keep bottles of insulin cool when traveling. Not refrigerator cold, but cooler than ambient temps. And they also sell these water retaining crystals for gardeners to help keep plants in window boxes and hanging baskets from drying out too quickly.

As for the neckerchiefs, they are better than nothing, but only just.