What is a HEPA Filter: 3 Working Methods Explained!

What is a HEPA filter? HEPA (pleated mechanical air filter) is an innovation above traditional filters. Let’s dive deep into the minute details of this type of filter!

A Quick Sneak Peek Into the Details:

A HEPA filter, also known as a high-efficiency particulate air filter, is helpful in cleaning and improving all the air from allergens and microbes.

  • It is made from special material constructed to stop as many pollutants as possible.
  • Whether you have an air conditioning system or an HVAC system, they most likely have a HEPA filter (or True HEPA) in them that captures particles of the size 0.3 microns.
  • It needs to be replaced when prompted by the device it is fitted into. You cannot expect the usage life of the filter to last a lifetime. The ideal time is 6 months to 12 months.

This article will further elaborate on how HEPA filters help us battle microscopic organisms that can trigger asthma symptoms or cause discomfort. Let’s get started!

What is a HEPA (High-Efficiency Particule Arresting) Air Filter?

HEPA stands for high-efficiency particle arresting, it is an air (pleated mechanical filter) filter that can get rid of 99.97% of dust, mold, bacteria, pollen, or any harmful airborne particles bearing a size of 0.3 microns (particle sizes).

Why is a filter called a HEPA Filter?

These filters are known for their HEPA filtration capability:

  • They are capable of removing particles that conventional filters have difficulty tackling.
  • While most filters will only trap larger particles, a HEPA filter will, without much effort, remove smoke and microorganisms from the air stream.
  • Another distinct difference is the material used to make the filter.

For more details on high-efficiency particulate air, check out this video:

YouTube video

Types of HEPA Filters

The HEPA filter is categorized into a total of 4 types.

  • True HEPA
  • HEPA
  • HEPA-like
  • HEPA-type

Working Process of a HEPA Filter

Created in a mat-like design with randomly woven fibers made out of borosilicate glass or plastic fibers, HEPA air filters specialize in capturing particles of various sizes.

What is a HEPA Filter? Working Process of a HEPA Filter

They allow particles of smaller sizes to pass through while stopping only the unwanted ones. Below are the type of particles they can capture!

Removal of Visibly Large Particles

Particles of larger size will not pass without colliding and sticking to the fiber of the filter.

Filtering the Small Particles

Flowing into the filter, these particles are stopped when they reach the size limitation in the filter, where they stick to the fiber and other tiny particles pass through.

Capturing the Smallest Particles

These particles are captured via Brownian Motion (diffusion), a phenomenon due to which particles are slowed down by colliding with gas molecules. They result in particles sticking to the fibers of the filter.

HEPA Filters and The Most Penetrating Particle Size

As stated by the Environmental Protection Agency (EPA), HEPA air filters can remove many microbes from the air. Still, the worst particle size that is considered the most penetrating particle size (MPPS) is 0.3 microns. To give you an idea of the size, here are some examples:

HEPA Filters and The Most Penetrating Particle Size

  • Dust mites (0.1-0.3 microns)
  • Textile Dust
  • Metallic particles or fumes (0.3-0.9 microns)
  • Fine Pollen
  • Auto Exhaust
  • Staphylococcus (0.3-0.9 microns)

Limitations of HEPA filters

A HEPA filter has several advantages but it also has its limitations. Here are some of them that you didn’t know!

Limitations of HEPA filters

  • They cannot get rid of odors.
  • Chemical gases are able to go through the filter without any restrictions. It cannot filter them as they are smaller particles than the holes on the filter.
  • Certain viruses are very small in size and can freely go through the filter and cannot be caught.

Filtration Process via HEPA Filters Helps Capturing Nanoparticles

Research conducted by NASA in 2016 confirmed that HEPA filters catch nanoparticles sized at 0.01 microns.

  • Further study also confirmed that a standard HEPA filter could capture airborne particles smaller than the deadly SARS-CoV-2 virus.
  • Researchers also found that this filter could be made more effective by adding a granular filter.
  • When this setup was integrated into an air purifier that had HEPA, it demonstrated outstanding HEPA filtration results.

Significance of HEPA Filter (Pleated Mechanical Air Filter)

If a family member suffers from severe allergies, asthma, or any other respiratory issue, then a HEPA filter can greatly impact their well-being:

  • The filters can easily remove triggering elements such as pet dander/human hair, or mold spores.
  • It screens out even bacteria and viruses.

If you are unsure about getting an air purifier with this type of filter, then checking the indoor air quality is the best way to ensure it!

Significance of HEPA Filter (Pleated Mechanical Air Filter)

Other reasons for the importance of HEPA filters are mentioned below!

  1. Smoke: HEPA filter can capture soot and very fine ash particles accumulating due to a forest fire nearby. It can reduce unhealthy levels of smoke indoors.
  2. Healthy Environment for a Patient: If the indoor environment requires super healthy conditions, then a hyper-HEPA filter can catch particles of 0.003 microns in size. Or, you can even use a HEPA air filter for microbes that are the size 0.3 microns (size range).
  3. Water Damage: A frequent flood or leakage in your home can damage the walls and spread mold. HEPA filters work to reduce the number of spores in the air and put a stop to the rapid spread.
  4. Volatile Organic Chemicals: These chemicals are lighter than air and may roam free indoors. The HEPA filters can filter them out of the air and ensure no such chemicals are left.

Changing a HEPA Filter in Air Purifiers/Vacuum Cleaners

Most of the time, you may notice a visible buildup (particle sizes) on the filter media. But, most air purifiers come with a pre-filter that usually filters out the larger particles.

So, the collection is usually a large number of microbes and other particles. In such a scenario, always purchase a new pre-filter before you discard the old one.

Changing a HEPA Filter in Air Purifiers_Vacuum Cleaners

Note: Most HEPA filters are washable but for those that aren’t, you need to change it too. Here is what you have to do!

  • Turn off the device/unit.
  • Search for the access door, usually on the back or side of the device/unit.
  • Carefully remove the old filter.
  • Now, fit in the old filter, and you are ready.
Pro Tip: Most manufacturers recommend a time duration for filter replacement. But that may vary on the environment around the air purifier.

Read Also: Best Quiet Air Purifier: 10 Top Picks with Low Noise Levels Reviewed

Frequently Asked Questions

What is a HEPA filter used for?

HEPA filters are used for controlling contamination in industries dealing with sensitive products. They remove bacteria, pollen, dust, mold, and bacteria from the air.

What is the difference between a HEPA filter and a regular filter?

The main difference between both of them is that a HEPA air filter is made from a thin layer of glass fibers. In contrast, regular filters are made from cotton or polyester material.

What are the two disadvantages of HEPA filters?

The two disadvantages of HEPA filters are: they are very expensive to replace, and secondly, very small parts (smaller than 0.3 microns) may accumulate in the filter and start growing in it.

Are HEPA filters worth it?

HEPA filters are worth it! Regardless of the price, these filters can significantly reduce the number of bacteria, microbes, and pollution in the air. They ensure the clean air quality and the health of people.


HEPA air filters, especially true HEPA filters, are very common in air purifiers, vacuum cleaners, and HVAC systems. They are made of a dedicated type of material that is woven tightly to capture even the tiniest particles.

It is highly effective but we need to keep in that they have a lifespan too and need to be replaced so that air quality indoors can is maintained. Have you heard of HEPA filters before, and what’s your take on them? Do let us know about them in the comments section!