Originally Posted by SwampYankee

I don't know about -10, but I've got a 20yo Thermos (the ubiquitous green hammer finish with the plastic screw-on coffee cup) that I used to take sledding up in VT. If I preheated it with boiling water, it would keep soup hot through the 2 hr ride up and 4-5 hours of riding until we took a break for lunch.

I'm pretty sure they still make the model. I'd imagine with newer technology more modern ones might have better heat holding ability although there are far fewer replaceable parts.