HEPA air purifiers are highly efficient filters for indoor air. Their main purpose is to remove fine particles from the air, including PM 2.5 and PM 10 (with a diameter of less than 2.5 and 10 microns, respectively). HEPA is neither a brand or a trademark, but a grade of filters. The requirements for HEPA filter have been strictly outlined and are continuously maintained by international standards, namely by EN 1822-1: 2009 and EN 1822-1-2010. HEPA purifiers
are made to remove all types of dust particles, allergens of sorts (pollen, fuzz, fur, bacteria, mold spores, dander, smoke, perfume scents, kitchen odors, etc.) from the airflow.
The HEPA standard, in its broadest sense, has several filtering classes. The most common (and cheapest) of them is E10, and it implies the efficiency of trapping particles only 85% (in fact, only using inertia). The next one is E11 (95% efficiency) and E12 (99.5% efficiency). In fact, the filters ranging from E10 to E12 should be called not HEPA, but EPA. However, standards in various countries allow manufacturers juggle standards and names sometimes. With that being said, filters starting from E12 in efficiency can easily be recommended for purchase, as their efficiency is already at a sufficient level.
The next class is H13. This is a true HEPA that involves the collection of 99.95% of contamination particles from indoor air. That means - almost everything is "caught" from the air flow. Further increase in class does not make sense in everyday living conditions, because class H14 assumes an efficiency of 99.995%. The next group - ULPA, starting with class U15, means the efficiency of 99.9995%. So, as you may have already guessed, the difference is going to be very hard to perceive.