HQRP Wick Filter for Holmes Humidifier HWF75CS / HWF75 D / SF221 / HWF72 / HWF72R Replacement Coaster HQRP&reg; Humidifier Wick Filter Replacement + HQRP&reg; Coaster; Improves efficiency of the humidifier, traps mineral deposits from the water; Extended filter life with help of reinforced layer; Replace filter every 4-6 weeks, depending on usage and hardness of water; 2 weeks DOA replacement warranty!