S-class, Pre-motor and/or Exhaust Microfilters – S-class, Pre-motor and Exhaust Microfilters (S =“Schwebstoff” = airborne particles) are made from electrostatically charged, micro-fiber material, which attracts and captures dust particles from the airflow of the vacuum before and after it passes over the motor to cool it. Cooling the motor with superclean air increases motor life and reduces the possibility of maintenance, even after many years of use. Also, the exhaust air is cleaned to the highest level before being emitted from the machine. The S-class Standard requires filters to absorb greater than 99.9% of particles down to 0.3 microns in diameter. For comparison, 100 microns is the diameter of a human hair. Their advantages are a relatively open texture that allows smoother airflow for better suction performance, a longer life expectancy, and they cost less than HEPA filters.