What Is A HEPA Filter?

HEPA is an acronym that stands for High Efficiency Particulate Air. We defines HEPA filters as a filter having a minimum efficiency of 99.97% on 0.3 micrometer particles. HEPA filter’s paper media is composed of micro-glass fibers, synthetic fibers, or expanded film like polytetrafluoroethylene (PTFE) that are pleated back and forth like an accordion to form a tight and compact filter element with a large surface area. This tight pleating is required because the paper has a high resistance to airflow and the media velocity is usually in the range of 6 fpm (.03 m/s). HEPA filters work by forcing air through the media’s fine mesh or “net” that traps dangerous particles such as pm2.5, dust, pollen, pet dander, viruses, bacteria, and micro-organisms. The 0.3-micron standard is used in efficiency ratings, because it estimates the most difficult particles size for a filter to capture (MPPS). They are designed to target very small particles and are not intended to work like a typical membrane filter, where particles larger than a given pore size of a filter are captured. However, HEPA filters are often more efficient in blocking and filtering particles that are smaller than 0.3 microns and larger than 0.3 microns. HEPA filters are a type of mechanical filter, which captures particles in four different filtration mechanisms based on particle size and velocity, which include inertial impaction, interception, diffusion, and straining.