i've done a few rides where I put warmer than average liquid into a sports cold beverage drinking container. Most time I could get out of a standard diameter container that fits in the typical frame mounted bottle cage is about an hour in Michigan's typical winter conditions. The wider the bottle [without losing length] the longer it lasted. I've slid a low volume {camping beverage container} double walled SS thermos in a plastic capsule I made using some SCH 20 pvc & glued on service caps. It was a conundrum for use, but the time before it lost it's BTUs increased by at least 25%, maybe more as IIRC the conditions were more frigid than usual, as that was my determination in creating something as such. I try to avoid those colder rides that would brick a typical one time use 16.9oz water bottle within an hour. Too much to contend with on the road/pathways as it is & those cold rides just are not enjoyable.
If you have a rechargeable pair of hand/feet warmers, I suggest that as an option to try. I've wrapped one of the foot warmers around a one time use bottle along with its small battery bank & put a can koozie over the complete assembly. Looks aren't going to win you anything, but you'll have a warmer drink.
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