Re-useable pocket hand warmers...

[Matt Weir]

I bought a pair of re-useable pocket handwarmers for £2 from Au Naturale on the Middlesbrooke Retail Park in Horwich yesterday (at the side of Bolton Wanderers Football ground). I think there are a few outlets not sure if it is only a North West based company though.

They are the type where you pop the metal disk and they chrystalise and get toasty and last for around an hour so ideal in this weather when you're out on a walk.

You put them on a rolling boil for 10 mins to reset them.

Matt.

 

[Mikey P]

You put them on a rolling boil for 10 mins to reset them.

I didn't know you could do that. How does that work, then?

 

[Matt Weir]

Not sure on the technical bit Mikey, not even sure whether its chemistry or physics really but it works. I boiled them last night whilst cooking and they look like ice melting in a bag. They turn back into a liquid state ready to go.

Matt.

 

[Bisamratte]

I have four of these and they are excellent. they are also good to use when you have a stiff joint that needs warming.

I think the metal tab creates just enough heat to trigger an exothermic chemical reaction. Heating it again when its crystallised returns the chemical to its liquid state. Or I think that's how it works....its been a long time since I did chemistry

 

[scanker]

I looked this up recently, so know it works because it's a supersaturated solution and the exothermic reaction is triggered because of a tiny bit of metal breaking off the activator strip.

http://www.stevespanglerscience.com/experiment/00000078

 

[Toddy]

They are wonderful
Take two with you on the coldest night; you know that wake up cold, damp and chilled to the bone, need to get up to p and soooo don't want to get out of your shivery nest in the heart of the night, feeling?
Get up, go p, shiver back into bed, crack one of the handwarmers and cuddle it against your chest.........blissfully go back to sleep Wake up again, chilled and damp, still too early to get up, crack the second one and doze peacefully for another couple of hours

Seriously, they're a little bit of heat that just makes a great difference to the comfort value of a good sleep on a cold, wet night.

Also recommended for inside pockets on your jacket on hanging around getting colder and nothing done, days; aching backs and knees and tooth and earache

Easy to re-charge too, just make sure the billy's big enough, when they go clear just let them sit in the hot water. I've got some I've been using for ten years. Might not be bushcraft but then, how purist are we, really?

atb,
Toddy

 

[Squidders]

They are good but I stopped using them a while ago because the boiling for 15 minutes annoyed me every time... Now I use the ones that take the fuel sticks...nice!

 

[led]

I stopped using mine when I put it on to boil and forgot about it until the smoke alarms went off

 

[Squidders]

 

[swyn]

As we steam our vegetables, a thought occured to steam this block back to liquid. Much quicker and less worry!
Swyn.

 

[Goose]

I have a couple of these and they do recharge in the microwave, but instructions say not to , I am careful when nuking them to put in for about 40 seconds a at a time then give them a squeeze to mix them and pop them back in for another 30- 40 seconds until they are clear all through. If you try them in the microwave yourself it is YOUR decision, the instructions on one set I have say not to heat in microwave and if they blow I don't want to be responsible for yours!
The reusable handwarmers don't work on an exothermic reaction they are a supercooled liquid. The liquid in them, which is a food additive and is technically safe to eat( I wouldn't try it though!) has a freezing temperature of (say) 40degrees C but because the liquid is pure and the inside of the bag is smooth no crystals can start to form and allow it to freeze. There is a small metal clicker inside that forms a first frozen crystal that allows the liquid to freeze, this is the clever bit, the liquid has to go UP to its freezing temperature to freeze! This would work with water too, but obviously a heat pad that rises to 0 degrees isn't much use! To reset the pad you have to take it past its freezing/melting point and ensure that ALL crystals have melted, then let it cool to ambient temperature that supercools the liquid again until the clicker is clicked to allow it to warm again to freeze.
I have melted these(reset them) in the window of a car in the summer.

 

[clcuckow]

I have used them for years and have loads (and have lost loads ) but then again quite a few of the pound shops around here (Warrington) sell them (normally two palm size one in a pack but no fleece covers for £1).

 

[clcuckow]

Found this link on how stuff works, on urrr... how this stuff works

http://home.howstuffworks.com/question290.htm

 

[AJB]

Yep, these latent heat of crystallization things are cool, and if you were in the shop around 2pm, I was probably standing next to you! It’s a small world.

Andy

 

[Matt Weir]

Yep, these latent heat of crystallization things are cool, and if you were in the shop around 2pm, I was probably standing next to you! It’s a small world.

Andy

LOL, I think it was about that time actually Andy! You didn't spot a big bearded ginger (strawberry blond )bloke wearing a Karrimor jacket carrying out a leather chair on his head did you?



Matt.