When you need max air flow reach for the Max-Filter? 2500 CFM. The objective when constructing the Max-Filter? was high air flow, convenience and effectiveness. The Max-Filter? has been constructed with lightweight aluminum (over 40% perforated) and high capacity carbon with an outside diameter of 20 in (over 17 sq/ft) of surface area. This large surface area allows for max air flow with an effective time in contact for odor and pollution control.