In a recent contest entry post, Clarence A. wrote: ‘Warm up some round river rocks that are as big as you can fit into a wool sock. When they are too hot to touch with your fingers put them in the wool sock and use them like you would a hot water bottle.’
No offense at your experience Clarence, but hot river rocks can hold moisture and can and do explode. I’ve had it happen camping as a kid, using a river rock for part of the fire ring, lucky no one was close when it exploded! it sent rock shards up to about 20 ft away. Please don’t ever use river rocks for [intense] heating- hot rocks do work great- but get them from some place dry like a stone wall! never use river rocks unless they have been high and dry for a while.
hot fist sized rocks wrapped in towels near your kidneys, and feet will provide about 4-5 hours warmth! I’d use the spit test, if it’s sizzles it’s ready. wrap them or put them in a sock, just don’t put it on your bare skin!
Good advice on socks, many thanks and much respect! – MFitzy in Pennsylvania