HWF65 is a cool mist humidifier wick filter, which fits models HM1840-UC, HM1845, HM1850, HM1851, and HM2060/W. It also features odor-absorbing technology. Holmes humidifier models HM3800 and HM3850 require 3 HWF65 filters. HM4000 humidifiers require 4 HWF65 filters, Holmes filters.