[Eyeless]

hopi it's a carbon filter..it has a duct and with the use of a fan the 'smelly' air is pushed through a screen of carbon..the "smell' sticks to the carbon and the air doesn't smell anymore... you normally need the fan blowing through this to be stronger than the fans blowing over your grow room...this way if more air is blowing through the filter than through the grow room... the air will always be "clean" this way.