How long do your vacuum flasks stay warm?Updated 2 months ago

As a rule of thumb, 6 hours, but this is variable and depends on the external circumstances. 

For a vacuum flask to work properly, it must have a high level of insulation between the two flasks, the outer casing and the inner flask. To minimise heat transfer, the space between the cylinders is a vacuum - a space without material. As a result, heat transfer between the inner liner and the outer shell is minimised and heat is retained inside the vacuum flask. This principle keeps your food and drink cool or hot, depending on what you put in the container. 

The inside and outside of the two layers are polished to absorb as little heat as possible and reflect it instead.