The air filtration system is the most important component of a cleanroom. The filters are designed to remove the particulates in the air down to sub-micron sizes. The standard High-Efficiency Particulate Air (HEPA) filter will scrub air down to 0.3 microns at an efficiency of 99.975%.
Working in conjunction with laminar air flow, multiple filters take out the amount of particles you need to meet your cleanroom standards. Laminar, or unidirectional, air flow, is a way of making sure that air flows in only one direction, lessening the possibility of particles getting kicked around and landing in your cleanroom. In most cleanrooms, air is directed from the top of the room to the bottom, ensuring any contaminating particles are pushed out, and don't have time to land in places they're not supposed to. Laminar air flow pushes air through the filters that remove it of particles. As air goes through filters, particles get stuck to the tiny, randomly placed fibers within the filter, and are thus removed from the air entering your cleanroom.