MERV 6 polyester non-pleated air filters provide between 20% and 35% efficiency for filtering particles between 3 and 10 microns in size (such as mold spores, dusting aids, and cement dust). They have a metal grid on both sides of the filter and capture contaminants more efficiently than MERV 5 non-pleated air filters.Non-pleated panel air filters are installed in HVAC systems to capture contaminants in the air stream. This improves indoor air quality and prevents the contaminants from building up in the equipment and damaging it. These flat air filters are commonly used to capture large particles between 3 and 10 microns in size (such as mold spores and cement dust). Non-pleated panel polyester air filters or fiberglass air filters are commonly used in furnace and central air systems in residential and commercial buildings. They are designed to be discarded when they are spent. A filter's MERV rating measures how efficiently it removes contaminants from the air stream based on the size of the particles it can effectively capture. The higher the MERV rating is, the more effectively the filter traps small particles.