The Horti-Control Dust Shroom is a reusable foam HEPA filter designed to keep unwanted pests and pollutants out of indoor gardens and air-cooled reflectors. Horti-Control teamed up with the leader in foam filter design for to create a filter for indoor gardeners. This revolutionary filter will keep your air cooled reflectors, inline fans, ice boxes, and ducting dust free. It will also keep mold, mildew, pests, and bacteria out of your garden! Choose between 4" or 6" dust shroom.