You could try making one by taping plastic bags to a glass bottle. The lid could be a problem, though a loose cork inside it and a flap of plastic bags hinged with a strip of tape would both help. a string and a notch could keep the lid-flap tight… It would be awkward to use and bulky…
P.S.
Having a hot thermos of pure water and another of hot soup sound like something that would really improve travelling. Just the feeling of home comforts while out in the world… There would also be some potential for medicinal benefits… If you put a hot rock in a thermos it would probably stay boiling for much longer… Consider also that a thermos can keep things cold. Between heat-absorbing chemical reactions and mechanical refrigeration, not to mention ‘cold spots’, it should be possible to chill things. You could keep an ice-pack in there to treat swelling and pain, ice cream to treat depression, liquid nitrogen to enhance coilguns…
There really needs to be some endothermic reactions, ice production, and an ice-cream recipe…