Reinforced design for longer life and better efficiency. Traps impurities in the water. Micro-free. Fits Holmes Humidifier Models HM-630, 729, 4600, 6000, 6000RC, 6005, 6600, 7203, 7203RC, 7204, 7305, 7305RC, 7306, 7306RC, 7405, 7405RC. Also fits Bionaire Models BCM645, 4600, 552ORC, 6000. 6010RC, 6610RC, 7203RC, 7204, 7207 and 7305/RC.