We test flasks and insulated mugs for the best coffee on-the-go.
We filled each flask with 95° C water and laid it on its side. Every four hours we decanted 300 ml into a tin cup, resealed the flask and measured the temperature of the water in the cup. All the flasks had an equal 1 ℓ volume and none of them, or the cups, were preheated. The test was conducted at room temperature.