The Aprilaire Water Panel 45 is a quality replacement filter for your Aprilaire 400 series humidifier. Also known as a media filter, humidifier pad, and evaporator pad, this product is paramount to deliver proper humidity to your home. Appropriate humidity in your home during dry heating seasons can alleviate allergy and asthma symptoms. Beyond these, it can also assist against dry nose, itchy skin, static shocks, and warped or cracked wood floors. To ensure the best performance the pad should be replaced twice a season and is available here as a complete-season 2-pack.