HEPA-13 is medical-grade purification technology that traps 99.97% of particles down to 0.3 microns, and 99.95% of particles down to 0.1 microns in diameter.Filters with a lower HEPA number (e.g. HEPA-11 and True HEPA) aren't as good at trapping particles, which means there are more contaminants in the air you're breathing at home.