HEPA (High efficiency particulate air Filter), means the filter efficiency reaches 99.97% against 0.3um particle.
The design of round HEPA filter is derived from the design of air purifier, the purifier is small and the filter height is limited. The advantages of round HEPA filter are lighter and relative smaller resistance, which is suitable for vacuum cleaners, air purifiers, etc.which have a limit on the height of filters.