Can-Filter Can 50 Pre-Filter Blocks pollen, dust, and other particulate from entering your filters. At a Glance Very low air resistance, easily changed. MERV-5 mesh blocks pollen, dust and other particulate from entering filter. Available in sizes for all filters. A clean Can-Filter® Pre-Filter is an excellent way of extending the working life of your Can-Filter® filter. The Can-Filter Group's replacement pre-filters extend the life of your Can-Filter. A pre-filter is the first line of defense against dust and debris clogging the pores of the carbon in your filter. The product's packaging allows for easy pegboard-style display.