This would not work in your thermos! This material is reflective in the visible but emissive in the infrared. The only thing that matters in the thermos is being reflective in the infrared.
Thermodynamics does not permit a thermal diode to exist.
Thermodynamics does not permit a thermal diode to exist.
This thermos would only keep your coffee hot if you dropped it into a furnace.
A perfect black surface on a spacecraft can do more than charcoal black paint, but only by a matter of degrees. If memory serves its less than a 2x multiplier between off the shelf and exotic materials. But when ounces cost thousands of dollars, you’re going to go exotic.