Y'all think it's feasible or worthwhile to get a metal flask from a thrift store to use as a hot water bottle for heating inside my jacket when I'm out in the cold?

Every winter I think about this but every winter I also live in an apartment with radiators I am not in control of or paying for.

https://www.lowtechmagazine.com/2022/01/the-revenge-of-the-hot-water-bottle.html