Not all filters are created equal. Peak performance is only realized when genuine Vornado Carbon filters are used. Usually your carbon filter's ability to trap odors and gases decreases over time, and airflow becomes obstructed as debris builds up. To assure peak performance, it is imperative to change your filter(s) 4 times per year using only genuine Vornado filters. Others may claim to be compatible with Vornado units, but the Vornado Air Purifier is calibrated to achieve a 99.97% capture rate only when used with Vornado Filters. Fits Vornado Whole Room Air Purifiers model numbers AC300, AC350, AC500, and AC550. Contains two (2) genuine Vornado Carbon Pre-filters. Vornado disposable carbon filters require no cleaning and are easy to replace, no tools required.