[micomonito]

Hello,
I take Design and Technology at school (I'm in the UK) and am working on a design project regarding helping the elderly stay warm- my aim is to focus on the elderly with mobility issues, making hand warmers that are contained in thin padding for use on handles of zimmer frames and the like.

The trouble I'm having is finding a good material for heating- this needs to be very easy to use.
I've focused mostly on sodium ethanoate, but it doesn't last as long as I'd really like it to (2-3 hours). They are reusable which is what I need, but the method required wouldn't be ideal because you need to boil them and bend an activator metal, which would prove a challenge for someone who might not have good dexterity.

Also things like iron powder, but hand warmers with those are single use and so wouldn't really be feasible.

I'm essentially looking for a material I can use that will:
- Get to a moderately high temperature (40 degrees?)
- Will stay reasonably warm for a couple of hours
- Is thin and flexible, so will fit in the small padding
- Is easily reheatable for an elderly person

I think I could make sodium ethanoate last long enough with insulation, but the reheating method just isn't ideal. What can I do? Optionally, I've thought about using a heated circuit, but have a pretty lacklustre knowledge of how I could make such a thing. Is there something else that fits this description that I haven't considered?

Thank you!!

[Borek]

I would look for solutions used in electric blankets. Chemistry based warmers are reasonably good in the field, where there is no other ways.

[marquis]

The iron powder ones can be cheap, although activation is not as easy as it seams.  They have to be packaged in nitrogen, particle size needs to be closely controlled, an some of the iron may have to be " activated".  Much more common are the common "gels", which are often packed in something like polyethylene and can be microwaved. Be careful with microwaving, though.  It is easy to overdo it and end up with a mess. Water over 140 degrees F will get into burn issues quickly ( always a legal issue, so be careful).