DUAL STAGE Pre-Filter Kit for MAC Air Helmet Pumper provides improved air filtration with two additional layers. The open cell intermediate foam filter catches the stuff that stops air flow and extends the life of the filter. The outer micron pre-filter is the first line of protection to stop most particulates from entering air flow. Compatible with BLOWER-FILTER-3R, BLOWER-FILTER-3-AC-R and improves filtration on any 3in tall MAC filters. Both filters are reusable and washable. Keeps the dust out and the air flowing. Includes washable foam intermediate filter and pre-filter.