This is a High Quality 2PK Humidifier Filter Water Panel Pad Designed To Fit Aprilaire Humidifier Models 110, 220, 500, 550, 558. Compare To Aprilaire 10 Water Panel Part. * Note Every Filter Panel has a black mark indicating which is the top of the panel when reinstalling into Humidifier. The pad is constructed of an expanded aluminum honeycomb mesh that is dipped in a clay coating. This coating is able to absorb and hold water. Warm, dry air is forced through the wet pad to introduce water vapor into the home. For optimal performance, we recommend to change your water panel every 3 to 6 months ( especially during humidifier season ) If not changed within recommended time period, the water panel will eventually become clogged with mineral deposits so less evaporation takes place. The result is less humidification.2 Aprilaire #10 Humidifier Water PanelThis humidifier filter (AKA water panel, water pad, evaporator pad) dimensions are approximately 9-1/2" x 9-3/4" x 1-1/2". This item comes in bulk and is designed & manufactured by Crucial Vacuum / Crucial Air.Fits the Following Humidifiers: Aprilaire 110 Aprilaire 220 Aprilaire 500 Aprilaire 550 Aprilaire 558 This is a generic product designed and engineered in the United States by Crucial Vacuum / Crucial Air. This is not a Aprilaire® OEM product and is not covered under any Aprilaire® manufacturer"s warranty. The Aprilaire® brand names and logos are the registered trademarks of their respective owners. Any use of the Aprilaire® brand name or model designation for this product is made solely for purposes of demonstrating compatibility.