Chemex Coffeemaker CoverChemex
Do you really need one? Perhaps... Want? Definitely.
A perfect balance of form and function, this glass cover keeps coffee at the proper strength by preventing evaporation.
Will it keep it hot longer? Marginally. Leave your Chemex on a slightly warm stove after boiling water (maybe not on, but near the element).
Great coffee always changes in interesting ways as it cools, so if it's Monigram Coffee don't worry about the heat too much.