Product contains 4 premium 2022 upgraded Honeywell Humidifier Filters for Filter A, HAC-504, HAC-504AW, and HAC504V1. The best wicking filters for Honeywell humidifiers..We manufacture our filters by utilizing a special interweaving locking pattern in order to keep the filter rigid and upright, even when soaking wet. Our competitors don’t do this and use cheaper manufacturing methods that leads to worse performance..Designed to fit the following Honeywell Humidifier Models: HCM350W, HCM-350, HCM350, HCM-350B, HCM350B, HCM-350W, HCM-350B-CST, HCM-300, HCM300, HCM-300T, HCM300T, HCM-305T, HCM305T, HCM-310T, HCM310T, HCM-315T, HCM315T, HCM305BCST, HCM-450B-CST, HCM450BCST, HCM-500, HCM500, HCM-530, HCM530, HCM-535, HCM353, HCM-535-20, HCM53520, HCM-540, HCM540, HCM-550, HCM550, HCM-550-19, HCM55019, HCM-551, HCM551, HCM-560, HCM560, HCM-600, HCM600, HCM-630, HCM630, HCM-631, HCM631.Our filters are treated to increase filter length but the exact time to replace the filter will vary based on your water and air quality. To increase filter length: use cold distilled water, flip daily, and soak in white vinegar. If you have hard water, the filter be stained yellow..We are a USA based company and we know we sell the highest quality and best humidifier filters on Amazon. We stand by our products with an unmatched 5 year replacement warranty and full satisfaction guarantee!