High-Efficiency Particulate Air (HEPA) filters are made to get rid of 99.97% of particles that are 0.3 microns or smaller. This means that they can get rid of allergens like mold, animal dander, dust mites, and pollen from the air. These filters are commonly used in air purifiers and vacuum cleaners, providing cleaner air and reducing allergy symptoms for many individuals. In this article, we will explore the benefits and workings of HEPA filters, as well as how to choose the right air purifier for your needs.

What Makes a High Efficiency Air Purifier
What Makes a High Efficiency Air Purifier

How HEPA Filters Work

High-Efficiency Particulate Air (HEPA) filters are a marvel of modern technology, providing a high level of filtration for the smallest, as well as the largest, particulate contaminants. They are composed of a mat of randomly arranged fibers, typically made from materials like polypropylene, polyester, or fiberglass, with diameters between 0.5 and 2.0 micrometers. These fibers make a narrow, winding path for air to travel through. Particles are trapped in this path by three different mechanisms: interception, impaction, and diffusion.

The Three Mechanisms: Interception, Impaction, and Diffusion

Interception occurs when particles moving along the air stick to a fiber. This mechanism works on particles in the mid-range size that are not quite large enough to have inertia and not small enough to diffuse within the flow stream.

Impaction is when the larger air particles embed directly into the fibers themselves. Inertia works on large, heavy particles suspended in the flow stream. These particles are heavier than the fluid surrounding them. As the fluid changes direction to enter the fiber space, the particle continues in a straight line and collides with the media fibers, where it is trapped and held.

Diffusion occurs in a HEPA filter when gas molecules that are smaller than 0.1 microns collide with each other and are delayed in passing through the filter. The delay will make it more likely for the next two mechanisms to occur for those smaller particles.

The Efficiency of HEPA Filters

HEPA filters can remove 99.97%–99.99% of airborne particles that are equal to or smaller than 0.3 microns in size. The efficiency is rated based on the worst level possible, so think about it as 99.97% or better. The diameter specification of 0.3 microns corresponds to the worst case, the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency.

The Range of Particles Captured

HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to a fiber) through a combination of the aforementioned three mechanisms. They effectively capture a wide range of particle sizes, including tiny viral droplets, particulate matter, pet dander, dust, and dust mites.

The Role of Pre-Filters

In an attempt to extend the usage life of a HEPA, a pre-filter can be included in the setup, which helps to remove the larger particles, leaving the finer-sized particles to be caught by the HEPA filter.

The Applications of HEPA Filters

HEPA filters are used in applications that require contamination control, such as the manufacturing of hard disk drives, medical devices, semiconductors, nuclear, food, and pharmaceutical products, as well as in hospitals, homes, and vehicles.

The Maintenance of HEPA Filters

All air cleaners require periodic cleaning and filter replacement to function properly. Follow the manufacturer’s recommendations on maintenance and replacement.

Benefits of HEPA Filters

  1. Allergy and Asthma Relief: HEPA filters can help soothe allergies and asthma by removing allergens and irritants from the air, providing relief from symptoms, and improving overall indoor air quality.
  2. Preventing the Spread of Infections: Some HEPA filters are designed to capture bacteria and viruses, potentially reducing the spread of infections in indoor environments.
  3. Improved Sleep: Cleaner air can lead to better sleep quality as allergens and irritants are removed from the air, reducing congestion and breathing difficulties during the night.

Choosing the Right Air Purifier

When selecting an air purifier, consider the following factors:

  • Clean Air Delivery Rate (CADR): This metric indicates the purifier’s ability to clean a specific volume of air per minute. A higher CADR means faster and more efficient air purification.
  • Room Size: Ensure the air purifier is suitable for the size of the room in which it will be used. Most air purifiers are designed for specific room sizes, so choose one that matches your needs.
  • Filter Replacement: HEPA filters need to be replaced periodically to maintain optimal performance. Check the manufacturer’s recommendations for filter replacement frequency and factor in the cost of replacement filters when choosing an air purifier.
  • Noise Level: Air purifiers can generate noise, especially on higher settings. Consider the noise level of the purifier and whether it will be disruptive in your living space.
  • Additional Features: Some air purifiers include additional Features such as activated carbon filters for odor removal, UV light for germicidal purposes, or smart controls for remote operation and monitoring.


HEPA filters offer numerous benefits for improving indoor air quality and reducing allergy and asthma symptoms. By understanding how these filters work and considering the factors mentioned above, you can choose the right air purifier for your needs and enjoy cleaner, healthier air in your home.


Hey there, I'm Kevin, editor of Xievo. I'm passionate about air purifiers and providing accurate information to help readers make informed decisions. In my free time, I love hiking and experimenting with air purifiers in my own home. Thanks for visiting Xievo!

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