There are even commercially available prototypes of that vacuum cooling technology, if you want to perform your own experiments with that concept: https://www.amazon.com/Thermos-Stainless-Ounce-Drink-Bottle/...

To be fair, they have mirror surfaces inside. A more realistic prototype would be ultra-black for something like 10-50x better radiative heat transfer. Of course it would still be more like shitty insulation than like good conduction.

That's my water bottle. 10/10 would recommend for not passing temperature gradients.

this kind of sarcasm will go over their head. People truly don't understand vacuums