Phat Filter, 4" x 20", 350 CFMKeep your grow room smelling fresh with Phat Filter. It uses virgin activated carbon (the best carbon on the market) to eradicate particles and odors from the air effectively. We have a laboratory test number to prove this. Here is the simple math: Carbon quantity * carbon quality = Filter capacity Quantity: The thickness of the carbon bed is 2 inches. So, it packs more carbon into the filter. Quality: The quality of the Phat filter is backed by