How HEPA Filters Work
HEPA stands for high-efficiency particulate air.
A HEPA filter is a type of mechanical air filter; it works by forcing air through a fine mesh that traps harmful particles such as pollen, pet dander, dust mites, and tobacco smoke.
HEPA filters in vacuum cleaners tend to use two quite different mechanisms to clean the airstream.
First, there are one or more outer filters that work like sieves to stop the larger particles of dirt, dust, and hair. Inside those filters, there is a concertina of what looks like folded paper designed to trap the smaller particles.
It uses three different mechanisms to catch dust particles as they pass through in the moving airstream. At high air speeds, some particles are caught and trapped as they smash directly into the fibers, while others snag on the fibers as they try to brush by.
At lower air speeds, dust particles tend to wander about more randomly through the filter and may stick to its fibers as they do so.
Together, these three mechanisms allow HEPA filters to catch particles that are both larger and smaller than a certain target size.