This Lo-Pro 4 in x 20 in 125 CFM Phresh Filter™ is a state-of-the-art carbon filter that cleanses the air to make it clean of dust, foreign particulates, organic compounds and odors. Phresh Carbon Filters™ are half the weight, and last twice as long because they are made with the unique properties of a 6mm (1.8") RC-48 activated, certified virgin Australian activated carbon bed that is machine packed. These Phresh Filters also optimize air flow with a cone shaped internal base, an "Anti-air Bypass" system and 51% open air custom mesh. They are used in research labs, plant breeding, tissue culture, indoor gardening, backyard & commercial greenhouses for their total airstream filtration characteristics. Phresh Carbon Filters™ are professional-grade systems designed to meet the demands of serious hobby and commercial growers. Flange & prefilter included. Additional Sizes Available.