What is True HEPA filter? True HEPA filter vs HEPA-type filter

If you have an air purifier, you may come across the term “True HEPA filter.” In fact, the True HEPA filter is widely acknowledged as the most popular air filter in both classic and modern air purifiers. This air filter is also the most important key factor determining the performance of an air purifier.

However, in real-world use, you may be misled by many air purifier brands that claim to have a True HEPA filter. The problem is, you don’t know if all the “True HEPA filters” are the same or if there are specifications to separate the class of these HEPA filters by value. Other results on the Internet don’t satisfy you, and you still can’t find one good True HEPA filter.

Don’t worry!

At Breathe Quality, we know all about your problems with indoor air quality and air purifiers. We know that you need the best air purifier to improve your quality of life. We are the experts in the field of air purifiers, but more than that, we are just like you, a human. We also have serious problems with airborne allergies and asthma, and we know your struggle to learn how to use the air purifier and put an end to your misery. Today, you will know everything about the True HEPA filter in our in-depth guide.

If you have concerned about other air filter types as well, we hope that the below guides can help you.

1, Ionizer.

2, Activated Carbon filter.

3, UV-C light filter.

4, PlasmaWave.

Get ready to know more about the True HEPA filter? Great! Keep reading.

What is True HEPA filter?

True HEPA filter, with HEPA stands for High Efficiency Particulate Arresting, or High Efficiency Particulate Air, is the highest standard for physical air filtration being used by the air purifiers. Moreover, HEPA filters are used in many applications, like vacuum cleaners, automobiles, and even aircraft.

However, to be considered a True HEPA filter, one HEPA air filter must be certified to remove 99.97% of all microscopic particles as small as 0.3 microns in size, which is the tiniest particle size to get into your lungs. Microns, which are one-millionth of a meter, are how particles are measured. To help you know the size of a micron, we are unable to visually see anything smaller than 10 microns. Also, the sizes of particles such as dust, pollen, bacteria, viruses, and many more are listed below.

Particle Particle Size (microns)
Atmospheric Dust 0.001 – 40
Bacteria 0.3 – 60
Beach Sand 100 – 10000
Burning Wood 0.2 – 3
Cement Dust 3 – 100
Clay, fine 0.5 – 1
Coal Dust 1 – 100
Combustion 0.01 – 0.1
Dust Mites 100 – 300
Fly Ash 1 – 1000
Grain Dusts 5 – 1000
Household dust 0.05 – 100
Human Hair 40 – 300
Insecticide Dusts 0.5 – 10
Lead Dust 0.1 – 0.7
Mold Spores 10 – 30
Pet Dander 0.5 – 100
Pollen 10 – 1000
Smoke 0.01 – 0.1
Tobacco Smoke 0.01 – 4
Viruses 0.005 – 0.3

In our list of the best air purifiers, there are only air purifiers with True HEPA filters.

The True HEPA filter is mostly made of highly dense paper, which is composed of very thin fibers with distances between 0.3 and 2.0 microns. The fibers are distributed randomly and oriented in all directions. There is a common assumption that the air space between the fibers must be as small as 0.3 microns, so the True HEPA filter can capture everything that is larger than this size. However, it is incorrect and impractical. With the smart design, the True HEPA filter can target the ultra-fine particles with a combination of three physical mechanisms:

  1. Inertial Impaction. The unclean air flows through the filter media of the True HEPA filter, but the heavier particles (or larger particles of pollutants) cannot follow the gas flow streamline. Imagine that, with their large inertia, these heavier particles travel along a straight path and will soon be captured by one of these fibers in the True HEPA filter. That’s why the fibers must be distributed randomly. So the larger the objects are, the more chance they have of being captured by the inertial impact mechanism of the True HEPA filter.
  2. Interception. This mechanism involves particles of somewhat smaller size, so they can easily follow the streamline and won’t collide directly with the fibers of a True HEPA filter. However, the radius of these particles is still larger than the distance between the streamline and the edge of the fiber (which is commonly 0.3 to 2 microns). Therefore, it will be captured by the edges of the fibers.
  3. Diffusion. This mechanism is the most important part of the True HEPA filter and can remove even the smallest particles. Once the particles are as small as 0.3 microns, they don’t strictly follow the streamline and can move randomly due to the collision with the gas molecules (Brownian motion). So the smaller the particles are, the higher their freedom of movement, and therefore, the higher the probability that they will encounter the fiber. The diffusion mechanism becomes more important as particle size decreases.

So to determine the total efficiency of one True HEPA filter, you must count the results of all three filtration mechanisms.

Are all HEPA filters the same?

No, not all HEPA filters are the same. There are significant differences in the HEPA filters being made by many air purifier brands. Depending on the quality of the materials as well as the density of the HEPA filter’s fibers, one HEPA filter may be different from another.

For example, Blueair uses a unique technology named HEPASilent, which improves the efficiency of the ionizer. The ionizer causes an electrostatic charge to build up on the particles on the fibers, just like what happens on a cat’s fur. Rabbit Air uses the BioGS HEPA filter to prevent the buildup of airborne particles, as well as the growth of bacteria and viruses on the surface, to improve both the efficiency and prolong the lifetime. Or, IQAir invents the HyperHEPA air filter with nanofibers to decrease the size of airborne particles to only 0.003 microns.

In the air purifier market, there are a lot of terms like “HEPA-type” or “HEPA-like,”  and they are totally inferior to the “True HEPA filter.” These filters can only capture particles as small as 2-5 microns, representing a 600% reduction in efficiency over a single True HEPA filter. To summarize, the best practice is to always seek out air purifiers with true HEPA filters.

But how do you know if an air purifier has a True HEPA filter? First, it must meet strict standards set by the U.S. Department of Energy. The True HEPA filter needs to remove 99.97% of all particles that have a size greater than or equal to 0.3 microns, as defined by the United States Department of Energy (DOE). You should search for the HEPA class in your air filter, which either follows the European Standard or the MERV rating. Below is the given efficiency of these HEPA classes for airborne particles down to 0.3 microns, which follows the European Standard:

HEPA class Efficiency
E10/H10 85%
E11/H11 95%
E12/H12 99.5%
H13 99.97%
H14 99.975%
U15 99.9975%
U16 99.99975%
U17 99.9999%

You can also follow the MERV rating, to decide the efficiency of HEPA filter:

MERV rating Dust Efficiency Particle size
20 ≥ 99.999% 0.1 – 0.2 microns
19 ≥ 99.99% 0.1 – 0.2 microns
18 ≥ 99.97% 0.1 – 0.2 microns
17 ≥ 99.97% 0.3 microns
16 ≥ 99.95% 0.3 – 1 micron
15 ≥ 95% 0.3 – 1 micron
14 90 – 95% 0.3 – 1 micron
13 89 – 90% 0.3 – 1 micron
12 70 – 75% 1 – 3 microns
11 60 – 65% 1 – 3 microns
10 50 – 55% 1 – 3 microns
9 40 – 45% 1 – 3 microns
8 30 – 35% 3 – 10 microns
7 25 – 30% 3 – 10 microns
6 < 20% 3 – 10 microns
5 < 20% 3 – 10 microns
4 < 20% ≥ 10 microns
3 < 20% ≥ 10 microns
2 < 20% ≥ 10 microns
1 < 20% ≥ 10 microns

Can you wash HEPA filters?

If your HEPA filter is not specifically labeled as washable, then the answer is no; you can’t wash your HEPA filter without damaging it. Otherwise, you can clean the air purifier’s filters without replacing them, but you need to know how to clean the air filter.

List of the best air purifiers

Pros & Cons of True HEPA filter

You have learned everything about the True HEPA filter, but you still don’t know if this air filter is flawless or not. Below is the pros/cons of the True HEPA filter.


  • Highly efficient, capture most of the toxic contaminants
  • Trapped particles will stay within the air filter
  • The physical air filter won’t emit ozone, which causes asthma and other breathing issues

  • Requires routine filter replacement to maintain the efficiency
  • Doesn’t remove odors and smell
Rating Breathe Quality
  • Average ratings for this post