I literally quote a person attributing the thermal insulation capabilities of vacuum flasks mono-causally to the lack of gas. I didn't imagine this, its right there to verify. Reminding people of laws of nature that have been known for 150 years and have withstood the test of time of investigation by physicists isn't "dunking on" anything, just reminding people of how the universe works.

The original vacuum flasks were made of glass, and a lot of laboratory grade vacuum flasks and Dewars are still made of glass. The consumer level Thermoses eventually switched to stainless steel.