Micro rating is the measure of the pore size in the media and expressed as either ‘Nominal’ or ‘Absolute’. Rating means percentage of particles that filter can capture at a given size like 10 microns at 90% will remove 90% of particles 10 microns in size. Absolute means the removal of all particles at a given size and larger like 20 micron absolute will trap 100% of particles 20 microns or greater.