Replace your Presorb® Prefilter every 3 months with regular use. PreSorb® activated coconut carbon prefilter traps odors and other organic compounds. It also extends the life of the HEPA filter by trapping larger particles. Maintain the health and comfort of you and your family. Contains 4 filters. Vornado’s Automatic Filter Refill Program for Vornado Air Purifiers offer a convenient way to receive regular shipments of Vornado filters for your Vornado Air Purifier! Eliminate the hassle of remembering to reorder. Maintain the high efficiency of your Vornado Air Purifier by never running out of new filters. Receive FREE SHIPPING on all air cleaner filter refill orders when you set up a product subscription. Click the “Subscription Wizard” button above to set a customized schedule to receive your filters – conveniently billed automatically. This Presorb® Prefilter, part number MD1-0005/0006 works with models AQS25/35.