Holmes humidifiers add moisture to indoor air, thereby decreasing the susceptibility to illness and common colds that breathing dry air can cause. This HWF72/HWF75 replacement filter features an antimicrobial barrier by Microban that inhibits mold, mildew, and bacteria growth inside the humidifier. The stretchy, circular filter measures 7-3/4 inches wide by 32 inches in diameter, and fits Holmes console models HM3500, HM3600, HM3640, and HM3650. The filter should be replaced every 4 to 8 weeks, or as necessary depending upon water quality.