Most particulate Filters are referred to as either Nominal, or Absolute. In the case of both of these filters the results achieved are very application sensitive. It is important to remember that lots of very creative claims are made by some manufacturers about how their filter will perform.
Nominally Rated Filters capture most of the particulate of the assigned micron rating, or higher. In practice, the flow
rate has a great impact on performance. In most cases, the slower the flow, the greater the efficiency of the filter.
Pleated Microfiltration Nominal Filters available online:
Absolute Rated Filters capture a much higher percentage of the particulate matter. Some manufacturers consider 95% as absolute, while others consider 99%, 99.9%, and 99.999%. Different test protocols are used to determine exactly what is absolute for a specific application. Although it is tempting to say that you need an absolute rated filter keep in mind that it is usually much higher priced.
Pleated Microfiltration Absolute Filters available online: