an improved , compact and low - maintenance respiration humidifier of a simple design is proposed , which has an outer jacket with a water feed as well as a breathing gas feed line and breathing gas drain line and contains a bundle of hydrophobic hollow fibers . the breathing gas feed line and the breathing gas drain line are in a gas flow connection with the interior of the hollow fibers . the hollow fibers preferably include polytetrafluoroethylene and have structure for electrical heating on their outer , water - side circumferential surface .