Cleanroom pre-filters offer an efficiency rating that determines their ability to capture particles of a specific size. The efficiency rating is typically expressed in terms of the filter's Minimum Efficiency Reporting Value (MERV). MERV ratings range from 1 to 20, with higher ratings offering better filtration efficiency. Generally, a higher MERV rating indicates that the filter is more efficient at capturing smaller particles.

Cleanroom pre-filters are made from different filter media, including synthetic fibers, paper, glass fiber, and activated carbon. Synthetic fiber filters are common because they have excellent holding capacity and filtration efficiency. Paper filters are less expensive and effective at capturing large particles, while glass fiber filters have a high dirt holding capacity. Activated carbon filters are used to remove gaseous pollutants and unpleasant odors.