This high quality humidifier filter is made of wick material that has been treated with Micro-FREE antimicrobial agent to extend filter life. It also has a metal mesh in the center to maintain its shape and provide maximum efficiency longer. The filter should be inspected for wear bi-weekly but should last six to eight weeks depending on water condition and amount of use. Detailed replacement instructions are included on the side of the box. This high quality replacement filter is manufactured by RPS products. For additional savings, we offer this product in a 6-Pack. (See listing at bottom of this page.) This product contains two filters.