The Horti-Control Dust Shroom is a PATENTED reusable foam filter designed to keep unwanted pests and pollutants out of indoor gardens and greenhouses. Horti-Control teamed up with UNI filter, the world leader in Foam filter design to manufacture Dust Shroom. Each size was engineered on a flow bench to exceed the cfm rating of inline fans to keep airflow loss to a minimum. This revolutionary filter will keep mold, mildew, pests, pollen, and bacteria out of your Grow tents, vertical gardening airflow systems, greenhouses, and areas that require air exchange!