What is a HEPA?
HEPA definition - Short for high-efficiency particle air, HEPA is a particle-absorbing filter that can remove very small lead particles and prevent them from being redistributed into the air. Common in vacuums.
Ideal Home Garden Explains
A HEPA is a filter made of small fiberglass fibre. This filter protects against small pollutants that may get pass ordinary filters. The filtration system goes through a three step process that includes interception, impaction, and diffusion. HEPA's are so effective that they have been known to catch particles that are invisible to the naked eye.