MPPS is the size of the particles that achieve maximum Penetration is a measure, in percent, of the material passing through a filter. Mathematically, penetration is 100 minus Efficiency (percent). If a filter is 98% efficient, its penetration is 2% (1 00 - 98). Penetration is used to measure the performance of very high efficiency filters.... of the The permeable material that removes particles from a fluid being filtered.. Particles that are smaller or larger than the most penetrating size exhibit a lower rate of penetration; the reduced penetration of the smaller particles is due to diffusion mechanisms, while for the large particles it is due to Interception is the process in which a particle is removed from an airstream as it follows the streamlines around a fiber. The particle comes in contact with a fiber and stays attached to it, because the van der Waal forces between the fiber and the particle are stronger than the forces of disruption of the moving airstream.... and inertial effects. The most penetrating size is a function of the structure of the filter medium, the Velocity is the distance traveled in a given time. Air velocity is measured in feet per minute (fpm or ft/min) in the English System and meters per second (m/s) in the SI System.... of the airflow through the filter, and the physical and chemical nature of the particles.