Hydrofarm Active Air Carbon Filter, 8"x 39", 950 CFMActive Air Carbon Filters are loaded with virgin activated Australian granular carbon. This carbon adsorbs VOC's (volatile organic compounds) therefore trapping every odor molecule that passes through the filter onto the micro porous carbon surface. These filters are light weight and incredibly effective at removing the most potent and dankest odors. Each filter is machine packed and includes a pre filter. ????? Attached flange ????? 1. 8" carbon bed