Active Air filters offer features and performance that rival the competition, all at a value price. All filters are maintenance free and feature long-lasting activated virgin charcoal that keeps your a odor-free. Corrosion-resistant galvanized steel , includes changeable Velcro pre-filter to collect dust and airborne particles .High grade activated charcoal to guarantee maximum odor control. Large surface areas and 2.5″ thick carbon bed. Charcoal is carefully packed to insure a consistent and even air flow throughout the carbon bed for a full usage of the filter and its durability and results in optimum odor control and maximum efficiency. Recommended airflow: 200 CFM minimum/400 CFM maximum.