What is a HEPA Filter and How Does It Work?

Written By: Dr Fahad Yasin

The term “HEPA filter” may sound perplexing, but it simply stands for “high-efficiency particulate air” filter. These filters, though invented in the 1940s during atomic bomb development, are actually quite simple in design. They consist of a mat of randomly aligned fibers made from either glass or synthetic materials, similar to those used in quick-dry T-shirts.

Table Of Content

Decoding the HEPA Acronym

HEPA represents High-Efficiency Particulate Air, a standard for air filter efficiency. However, it’s important to know that there’s a difference between a genuine HEPA filter and its counterparts like HEPA-like, HEPA style, or HEPA type filters.

The brands whose filters pass the HEPA test label them as True HEPA filters to stand out from misleading claims.

The Mechanism of HEPA Filters

  • For larger particles (above 10 microns), the filter acts as a net, straining and capturing particles stuck between its fibers.
  • Particles between 0.3 to 1 micron (e.g., bacteria) may follow the air around the fibers but can be intercepted due to their weight.
  • Particles smaller than 0.3 microns (e.g., nanoparticles) exhibit Brownian Motion, bouncing around and eventually adhering to the fibers due to diffusion.

HEPA Filter Composition

  • Glass-Based Filters: Fiberglass air filters are made from substances like silica, alumina, calcium oxide, boron oxide, magnesium oxide, and sodium oxide.
  • Synthetic Filters: These filters use materials similar to those used in quick-dry T-shirts, like polyester.

Variations in HEPA Filters

  •  HEPA filters are highly effective at capturing particles of almost every size, including viruses, bacteria, pollen, allergens, and PM2.5. They are considered the most critical component of any air purifier.
  • In Europe, HEPA filters must remove at least 99.95% of particles, while in the US, the requirement is even higher at 99.97%.
  • Filters capturing between 85% and 99.95% of particles are referred to as “EPA filters” or “efficient particulate air filters,” not meeting the strict HEPA standards.
  • Filters exceeding the HEPA requirements and capturing more than 99.999% of particles are termed “ULPA filters” or “ultra low penetration air filters.”

MERV Rating Explained

MERV, or Minimum Efficiency Reporting Values, is a rating system that measures a filter’s efficiency to capture particles between 0.3 and 10 microns. In the US, a HEPA filter must achieve at least a MERV rating of 17, while in the EU, a MERV 16 rating qualifies.

Distinguishing True HEPA from Other HEPA Filters

True HEPA filters are certified to meet the HEPA standard, unlike other filters labeled as HEPA that have not undergone or failed the testing phase. These non-True HEPA filters can filter 85 to 99% of airborne particles down to 0.3 microns. Their lower cost and reasonably good performance make them a viable choice for many consumers.

Pros and Cons of HEPA Filters

HEPA filters’ effectiveness has led to their wide usage in various sectors, including hospitals, homes, vehicles, and various consumer products.

However, their need for replacement and higher initial cost could be a deterrent for some. Furthermore, while excellent at removing particulates like dust, pollen, and mold spores, they are ineffective at eliminating odors and chemicals.

HEPA Filter Maintenance

Avoid washing and vaccuming HEPA Filters.

Health Benefits of Using HEPA Filters:

  •  By efficiently capturing a wide range of airborne particles, HEPA filters can significantly improve indoor air quality, reducing the presence of allergens, dust, pet dander, mold spores, and other harmful pollutants.
  •  People suffering from allergies and respiratory conditions, such as asthma, can experience relief and improved well-being in environments with HEPA-filtered air.
  •  HEPA filters are particularly effective at removing airborne viruses and bacteria, providing an added layer of protection against infections and diseases.
  •  Individuals exposed to high levels of air pollution, whether due to outdoor pollutants or indoor sources, can benefit from HEPA filters as they offer a sanctuary of clean air within their living spaces.





High-Efficiency Particulate Air


Originated in World War II; commercially available since the 1950s


Traps particles using direct impact, sieving, interception, and diffusion


Captures 99.97% of airborne particles down to 0.3 microns (US standard); 99.95% (EU standard)

Microns Explained

A micron is extremely small; for instance, there are 24,500 microns in one inch. HEPA filters can trap particles smaller than a single micron

Filter Construction

Made up of intertwined glass fibers arranged in a complex pattern


Different efficiency standards exist depending on the region (US vs. EU)

MERV Rating

Minimum Efficiency Reporting Values; a rating system for filter efficiency. US HEPA filters need a MERV of at least 17

True HEPA Filters

These are certified to meet the HEPA standard, unlike other HEPA-like filters


Highly efficient at removing particulates like dust, pollen, and mold spores


Regular replacement is necessary, they have a higher initial cost, and are ineffective against odors and chemicals


HEPA filters generally should not be washed or vacuumed as it can damage their delicate structure


Used in a variety of devices and sectors, including home appliances, healthcare, nuclear facilities, and the food industry


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