Originally Posted by
superslomo
When you use the chemical warmers, they last much longer than you actually need. If you put them in a plastic ziploc of some kind and get all the air out when you get home, they will be good for a few extra uses. They also don't stay as warm when there are booties over the shoes, as they need air with which to react to create heat.
When I use chemical warmers, I need them for 12 hours.
They don't last 12 hours ... 8 or 10 maybe.
I've only ever used them when I've done bitterly cold winter centuries.