We’re constantly inundated with buzzwords. Those like “natural,” “eco-friendly,” and even “HEPA” often make the list. All too often, we don’t have the time or background information to know exactly what these terms mean.


Because there’s money to be made and jargon that can be used to confuse consumers, “HEPA” is becoming the new “natural” label. Terms like “HEPA-type,” “HEPA-like,” or “99% HEPA” are similar to “All-Natural,” “Naturally Made,” or “100% Natural”—all of which lack real meaning. You may think you’re getting something that’s better for you and your family, but in fact, you could be putting them in harm’s way.


We’re here to clear the air and set the record straight.


That said, HEPA filters are not interchangeable with HEPA-type or HEPA-like filters. If you want the most effective kind of filter to provide clean, healthy air, only true HEPA filters can do the job. Let’s take a look at what HEPA actually means, as well as how the filters originated.

The Origin of HEPA Filters

HEPA filter systems were first developed in the early 1940s. They found their initial use in the Manhattan Project, the U.S. government research project responsible for the development of the first atomic bombs. HEPA filters played a key role by containing the spread of airborne radioactive contaminants.


Shortly thereafter, HEPA filters were introduced commercially. Because they were capable of capturing bacteria, fungi, pollen, viruses, and particulate matter (pet dander, dust, and smoke particles), they found use in many buildings.


As they continued to show promise in ensuring cleaner air, they grew in popularity. This was especially the case because more industries needed highly efficient air filters (hospitals, and the pharmaceutical, aerospace, nuclear power, electronics, and computer industries). Eventually, similar filters made their way into homes around the world.

What is a HEPA Filter?

First, let’s clear something up. True HEPA and HEPA are often used interchangeably and mean the same thing. “True” is used to help differentiate it from all those “HEPA-type” euphemisms out there.


So, what is a HEPA or True HEPA filter? HEPA stands for High Efficiency Particulate Air. A HEPA filter is capable of removing at least 99.97% of airborne particles like dust, mold, pollen, bacteria, and any others with a size of 0.3 microns (µm). In doing so, it meets U.S. standards, like that of the EPA and U.S. Department of Energy.

Why 0.3 Microns?

Industry standards revolving around testing at 0.3 microns do so because it’s considered to be the Most Penetrating Particle Size (MPPS). In layman’s terms, this means that the particles that fall between 0.2 and 0.3 microns are the most difficult to capture. With True HEPA filters, you can consider the 99.97% capture rate as the worst-case scenario, because particles both smaller and larger are more effectively captured.


Put another way, if a room contains 10,000 particles that are 0.3 microns in size, just 3 will escape a HEPA filter. Those that are of a larger or smaller size are removed at an even higher rate.

AirDoctor UltraHEPA air purifiers are able to capture particles 100 times smaller than the HEPA standard, meaning that they’re third party tested to remove at least 99.97% of particles as small as 0.003 microns (take note of the extra 0s)! Some of these smaller particles include:

  • Viruses (0.06-0.1 microns)
  • Bacteria (0.06-0.2 microns)
  • Smoke (0.1-1 microns)

What are HEPA Filters Made From and How Do They Work?

HEPA filter air purifiers essentially trap particles. The filters are typically made from a membrane of woven polymer fibers, laminated to a substrate. Randomly arranged, they create what could be considered a maze.

As particles enter this myriad arrangement and attempt to traverse the maze, they’re pushed through by a HEPA filter fan and captured in a few different ways.

  • Inertial Impaction: Thanks to inertia, larger contaminants, like some types of pollen, dust, and mold, simply travel in a straight line before colliding with—and sticking to—a fiber. Sieving will capture most partible except fine and ultra-fine particles 0.0 up to 0.5 microns
  • Interception: As the airflow makes its way around fibers, it pushes mid-sized particles that aren’t large enough for inertia into the sides of the fibers, leaving them stuck. Interception captures mid size of ultrafine particles that can escape between fibers of inertial Impaction
  • Sieving: The most common filtration mechanism, sieving works when the particles are simply too large to move between the fiber spaces.
  • Diffusion: The small, ultrafine particles move erratically and traverse the flow stream, meaning they’re likely to collide with the fiber and become trapped.

But What About HEPA-Type Filters?

Not all HEPA air purifiers are created equal. Unlike true HEPA filters, those promoted as “HEPA Like,” “HEPA Style,” “99% HEPA,”  or “HEPA type” fail to meet HEPA standards.

For most consumers, these terms are essentially meaningless. “HEPA type” or “HEPA like” are often used to manipulate consumers into making the purchase of filters and air purifiers that are of a lower quality. Saying that they’re similar to HEPA filters is misleading—filters are either HEPA, or they’re not.

While the amount that they do capture varies, it’s almost certain that these HEPA-adjacent filters can’t compare with the true HEPA filter’s capability of removing 99.97% of particles that are 0.3 microns in size.

Worse, often made with fiber structures that are less dense or constructed with inferior materials, these filters perform especially poorly when it comes to the smallest, most harmful particles. They may be capable of reducing the amount of pollen, lint, dust, or pet dander in a room, while leaving you exposed to particles that can lead to a lot more than just allergy symptoms.

Filters Can Also Come in Different MERV Ratings

As a reminder, HEPA filters are rated based on their worst removal efficiency. For true HEPA filters, this means that 99.97% of potentially harmful particles at 0.3 microns are removed.

Another way to look at the efficiency of a filter is through the MERV rating, or the Minimum Efficiency Reporting Value. A MERV rating demonstrates to consumers how efficiently a filter will remove airborne particles, based on a scale between 1 and 20. The lowest efficiency is given the value 1, while the highest receives a 20.

It’s important to note that anything with a MERV above 16 is typically reserved for pharmaceutical or electronics manufacturing, or use in nuclear power plants. Those with a MERV rating of 5-13 are what you’d look for for use in a home air purifier, with the higher MERV rating a better option.

Developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), we can understand the MERV ratings as follows:

    • MERV (1-4): Captures 60-80% of particles larger than 10 µm.
  • MERV (5-8): Captures 80-95% of particles 3.0-10.0 µm.
  • MERV (9-12): Captures >90-98% of particles 1.0-3.0 µm.
  • MERV (13-16): Captures >95-99% of particles 0.3-1.0 µm.

So, essentially HEPA filters exceed the ASHRAE Standard rating system. We can think of them as rating MERV 16+. These types of filters are often used in operating rooms and other indoor spaces that need optimal air filtration. That said, they’re too much for homes and residential spaces, which is why commercially sold air filters have MERV ratings of 11-13 instead.

AirDoctor Filters

AirDoctor uses H13 UltraHEPA® filters. This is a grade of filter material that is used by the HEPA filter membrane industry. It reflects the calcification (hardening) of the filter material before it is assembled into a filter frame and tested to the HEPA standard.

AirDoctor’s UltraHEPA® filters are independently tested and proven to remove ultra-fine, airborne contaminants like bacteria, viruses, smoke, pet hair and dander, pollen, dust, and mold spores. Remember, these ultra-fine particles are also those that are most hazardous for your health, which is why genuine AirDoctor filters are the best bet for your peace of mind.

What to Consider Before Buying a HEPA Filter

TL;DR: a filter is either HEPA or not. It should only be considered as such if it meets or passes the HEPA standard test.

If you’re in need of a HEPA air filter replacement, look for the details. As we mentioned in our recent blog, you should check for claims of 99.97% removal of particles the size of 0.3 microns—and be sure to look for proof of independent testing! As always, AirDoctor’s here to help by taking the guesswork out of clean air.

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