Mechanical
Mechanical air filters remove particles from the airstream because particles come in contact with the surface of fibers in the filter media and adhere to the fibers. The mechanisms by which the particles come in contact with the fibers in the filter media is covered in the air filter mechanisms section.
There are two broad categories of mechanical air filters:
Fine Fiber Media Air Filters - These filters utilize filter media with fibers small enough in diameter to allow for the capture of sub-micron particles at high efficiencies without the necessity of electrostatic attraction. Fine fiber media is often made of glass fibers or PTFE.
Coarse Fiber Media Air Filters - These filters utilize media with large diameter fibers which normally wouldn't allow for the capture of sub-micron particles at high efficiencies. To increase the particle capture efficiency, an electrostatic charge is placed on the media to provide for electrostatic attraction to particles. Coarse fiber media is often made of synthetic fibers.
Electronic Air Cleaners
These filters require an external power source. The filters impose a charge on the particles in their first stage, and often use a set of parallel plates onto which the particles are collected in their second stage. The charged particles will be attracted to a plate of the opposite charge. On a regular basis, the plates need to be cleaned in order for the filter to retain its maximum efficiency.