Atmosphere PROfilters Reversible Carbon - 20"Most air filters utilize 65% of the carbon available by only filtering through the top section of the carbon filter, leaving the bottom section unused. PROfilter uses an innovative patented design allowing the user to reverse the filter, benefitting from the use of 100% of the carbon available and effectively extending the units life span. Manufactured with only the finest TC940 virgin 4 mm grain sized carbon, PROfilter effectively removes 99. 5% of