[EXCELLENT PERFORMENCE] - ①Our for hac-504 filter successfully filters impurities in the water and retain the mineral elements needed by the human body. While humidifying the air, it relieves the discomfort caused by the dry environment and moisturizes the skin. ②Prevents white a powder from entering the room air and depositing on everything in sight [THICK ABSORBENT CRAFT] - Our Upgrade humidifier filters for HAC-504 use strong and thick absorbent paper. The interlaced mesh structure allows water to pass through the voids to create capillarity. Therefore, our filter can reduce water evaporation to a greater extent and realize the high-efficiency water output of the humidifier. In addition, it can also improve the degree of hardening of the HAC-504 filter after exposure to moisture, thereby increasing the service life of the filter [COMPATIBLE MODELS] - Our HAC-504 humidifier filters fit for -350, HCM350,HCM350W, -350B, HCM350B, -350W, -350B-, -300, -300T, HCM300T, -305T, HCM310T, -315T, HCM305BCST, -450B-, HCM450BCST, -500, -530, HCM530, -535, HCM353, -535-20, HCM53520, -540, HCM550, -550-19, HCM55019, -551, -560, HCM560, -600, -630, HCM630, -631, HCM631 [] - Package includes 4 x Upgrade HAC-504 for humidifier filter. Our upgraded filters feature a blue pre-filter to catch large particles. Warm Tips: For best results, please fill the humidifier tank with distilled water. Excessive use of hard water degrade filters and cause them to turn yellow prematurely. We recommend you to replace the HAC-504 filter every 2-3 months for optimal performance (depending upon your usage)