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

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.

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

I absolutely don't understand how vacuum works. So I absolutely cannot model how a Dewar flask which has 15 billion light year thickness between the inner and outer wall - a wall that is very close to absolute zero will behave.