HQRP Wick Filter for Vicks V3500N, V3850, V3850JUV, V3900JUV Humidifiers + HQRP Coaster HQRP&reg; Wicking Filter Replacement + HQRP&reg; Coaster; Improves efficiency of the humidifier, eliminates minerals and impurities from the water, providing clean, fresh moisture. Extended filter life with help of reinforced outer layer; Replace filter every 4-6 weeks, depending on usage and hardness of water; 2 weeks DOA replacement warranty!