HEPA filters, known as high-efficiency particulate air filters, can remove almost 99.97% of pollen, dust particles, mold, bacteria & any air-borne particles. The thickness of human hair is 40 microns to 60 microns whereas HEPA filters can filter out small particles of even less than 0.3 microns. HEPA filters are efficient in filtering out harmful airborne particles & help in purifying the air around us. In the recent times of covid outbreak, HEPA filters have been proven effective against SARS-CoV-2 covid virus as well.
It might be on your mind what a HEPA filter looks like. Well here is the representation of a HEPA filter as it looks in Eco-1000(commercial air purifier):-
HEPA filter as in Eco-1000(commercial air purifier)
Brief History
The HEPA filter was not created in the form of a typical purifier unit. Invented during World War II around the 1940s, the first version of high-efficiency filters was in the form of a gas mask made of CC-6 paper created by the Chemical corps. Since using the gas masks at all times was impractical, the Army Chemical Corps created a mechanical blower and purification unit. In these purifiers, cellulose asbestos paper was customized into a pleated form, and spaces were provided between it for air to pass. Back then, it was referred to as the absolute filter, to what we now know as the HEPA filter.
Working of HEPA
The conventional ideology of filtration technique that we normally assume for a HEPA filter is that – the particles bigger than the space between the fibers might get stuck between fibers and smaller particles might pass on. Although this is true to some extent i.e., for bigger-sized particles that mechanism is referred to as straining. But the primary mechanisms on which HEPA filters work are Inertia, diffusion, and an interception.
HEPA ratings
In general, the air filters are classified on the basis of MERV (Minimum efficiency reporting values) ratings, rated from 1-16, with MERV 16 highest inefficiency. According to ASHRAE, HEPA filter efficiency is greater than MERV 16 . The classification of various types of HEPA filters and their efficiencies are tabulated below –
HEPA Filter: What can it do?
HEPA filters provide protection against certain unwanted elements in indoor environments, such as houses, offices, restaurants, etc. The classification of elements that can be removed by HEPA alone and when in combination with other technologies is as follows : 
All these details of what a HEPA filter can do are intriguing. But there’s still skepticism around one thing – Can HEPA filters remove Nanoparticles? The verdict – Yes, HEPA filters can remove nanoparticles as well; all thanks to the study conducted by researchers at the University of Minnesota. The results of the study showed that HEPA filters captured 99.99% particles of < 5-nanometer size.
Eco-1000 uses a combination of HEPA+Activated Carbon along with a photocatalyst filter and UVC light.
[1]https://www.osti.gov/servlets/purl/1363772
[2]https://www.researchgate.net/publication/226318339_Experimental_study_of_nanoparticle_penetration_through_commercial_filter_media
[3] https://www.cibsejournal.com/technical/understanding-hepa-filters/
