This Activated Carbon Filter (2-Pack) is designed for use in Vornado True HEPA Air Purifiers. Replace your carbon pre-filter every 4-6 months with continuous use, depending on your environment. This activated coconut carbon pre-filter 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 2 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 Activated Carbon Filter (2-Pack), part number MD1-0023, works with models AC300/350 and AC500/550 True HEPA Air Purifiers.