Word of warning, all lighter fluids aren't the same. Took me awhile to figure out the obvious, the reason my hand warmers sometimes worked and sometimes didn't was the fluid I was using. Zippo and Ronson work, some others also. Trial and error sucks, I've used more than few brands of lighter fluid that didn't work in my hand warmers as fire starter

I'm fairly cold tolerant, comfort isn't an issue. But I do need to be able to bend my fingers and not shiver when shooting.

The wife bought me a Lava Buns seat cushion. I was skeptical, but it was one of those pleasant surprises, it actually works as advertised.