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What Is a HEPA Filter?

HEPA Filters

A HEPA filter removes harmful particulates from the air. HEPA is an abbreviation that stands for 'High-Efficiency Particulate Air' and represents the top standards in the industry. Products with HEPA are often described as True HEPA, Medical HEPA, Super HEPA, etc. These terms or "HEPA types" are usually associated with numerical values that reference MERV Ratings.

What are HEPA Filters Made Of?

HEPA filters were first invented way back in the 1940s while scientists in America were working on the atomic bomb. A HEPA filter may sound quite complicated but basically, they are made using glass or synthetic fibers which are aligned during the manufacturing process. The filter itself is like a very dense matting that allows air to pass through it but the fibers it is made of stop the vast majority of air particulates from getting through.

What are HEPA Filters Used For?

HEPA filters were first commercialized during the 1950s and are now in wide-scale use. There's a surprising range of ways that HEPA filters are used including in the manufacturing process of disk drives, semiconductors, and medical devices.

They are also used in some food production techniques, by pharmaceutical companies, and even in the nuclear industry! However, primarily, HEPA filters are used in hospitals, vehicles, and home settings to remove harmful particulates from the air.

What Counts as a HEPA Filter?

To qualify as a HEPA filter it must meet the very highest industry standards. This is to guarantee their safety and to ensure the trust of the public in their utility. The strict requirements mean that in the USA a HEPA filter must remove X percentage of particles from the air at varying particle sizes per their stated  'H' classification scale. See MERV Ratings.

 

How To Clean HEPA Filter

Can you wash a HEPA filter? Although some people do attempt to clean their HEPA filters by rinsing them in water or even by using a vacuum cleaner to extract the trapped particles, this is not advised!

Even if you carefully wash a HEPA filter you may damage or disrupt the fibers in the filter which are supposed to stop the particles from getting through. Once the mesh of fibers has been damaged, even slightly, the filter is compromised and will not deliver the same level of protection.

It’s always a better choice to regularly replace a HEPA filter in line with the advice of its manufacturer.

How HEPA Filters Are Made

HEPA filters are made using glass or synthetic plastic fibers. These tiny fibers are made by melting the glass or synthetic material and then pushing it through the very fine pores of a nozzle that spins around. As the fibers are passed through the spinning nozzle they cool down and then form a hard web-like structure.

As the fibers are passed through the nozzle it is also moving from side to side. This creates an even, although random, matting of cooled fibers. The nozzle sprays the molten fibers onto a conveyor belt - the speed of which determines the thickness of the filter. The slower the conveyor belt is moving the thicker the filtering materials will be because there is more time for the webbing to be formed.

While the fibers are cooling they form bonds that create the structure of the filter material. A latex binding is often added at this point of the production process to increase the strength of the filter. Once the webbed matting has cooled and set it is folded over itself to improve the filtering ability of the materials. Lastly, the folded matting is placed in a casing - usually within a wire grid - and the HEPA filter is complete - ready to hit the market and start its life as a filter.

How Does a HEPA Filter Work?

HEPA filters work in several ways to remove the particulates from the air. One of the benefits of using a HEPA filter is that it is specially designed to be able to stop many different sizes of particles from passing through the air. This protects the user from breathing these harmful particles into their lungs where they can cause a wide range of health complications and difficulties.

  • Diffusion. A HEPA filter stops small particles, especially those beneath 1 micrometer, from passing through the webbing. These particles are stopped from passing through the filter by a similar process to Brownian motion - which says that the probability of a particle being stopped from passing through is very high. This process is more effective at slower speeds of airflow although it does still work with faster-flowing air.
  • Interception. Many of the particles that are in the air and flow through the filter will bump into the actual fibers of the filter. The particles will then attach to the fiber and be stopped from passing through. This removes them from the airflow and prevents them from going through and keeps the air cleaner.
  • Impaction. Large particulates in the air cannot pass through the fine webbing of the HEPA filter and are removed from the airflow. This works at any speed of airflow however it works best at faster speeds.


The process of removing particles under 1 micrometer is mostly done by diffusion while particles that are larger than 4 micrometers are removed by interception and impaction. Together, these three ways of removing particles cover a wide spectrum of the particles that are commonly found in the air and need to be removed.. 

HEPA Filter Limitations

While HEPA filters are fantastic at removing particles from the air they cannot effectively filter out gases or odors. Chemical vapors, such as cigarette smoke, will not be removed from the air by a HEPA filter. However, there are ways around this by using a HEPA filter in combination with other filters to remove these odors and gases from the air.

For example, you can use an Activated Carbon Filter  with your HEPA filter to remove gases, bad odors, and Volatile Organic Compounds (VOCs) from the air. These gases can include anything from smoke to the odor of pets! This combination makes for very effective air cleaning resulting in much better indoor air quality.

Best HEPA Filter Air Purifiers

HEPA filters are an incredibly effective way of removing particulates, dangerous or otherwise, from the air. Removing these particles from the airflow helps to keep your environment clean and reduces the risk of a variety of health problems that can arise if they get into your lungs and respiratory system.

To Learn More visit our Best HEPA Filter Air Purifier collections at Think Air Purifiers HEPA With Activated Carbon Collection.

These air purification systems typically use a pre-filter to capture larger particles (like a human hair) giving longer life to the HEPA Filter which removes smaller particles (like mold spores). They are used along with activated carbon to provide a powerful solution to indoor air quality concerns.