The metal portion should not be radiating heat. Implies there’s something not quite right with the vacuum seal. If it’s new, you might try returning it & asking for a replacement. If it’s only mildly warm, that might be normal - have you considered getting a knit hat to place over that area to further insulate it (yes, I’m too cheap sometimes).
FWIW, I’ve had great luck with my Stanley thermos for doing exactly what you’re doing, keeping coffee hot for hours. I also like Zojrushi’s products - I have a smaller one I use to keep my creamer cold.







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