The principle is simple: the white porcelain jug is accompanied by a perfectly fitting cover made of stainless steel, which is known to be a poor conductor of heat and is lined on the inside with felt (made of 100% polyester). This provides extremely effective insulation and whatever is in the pot - coffee or tea - stays warm for longer under the cover. By the way: the mantle jug is only available from us with the porcelain knob.