Holmes HWF75PDQ-U Wick Humidifier Filter Nullify Imported Improves efficiency of the humidifier Holmes Filter Fits: Holmes: HM-3500, 3600, 3640, 3650, 3655-White Westinghouse: WWHM3300, WWHM3600 Extended filter life with help of reinforce outer layer Extends product life as less mineral deposits will attach to the unit Antimicrobial Treated Customers may receive HWF75, which is the exact same product aside from a different packaging configuration