Overview: Types of Air Filters & What to Know

There are multiple types of air filters and technologies that exist to clean and filter the air we breathe. But what type of filter should you use for filtering viruses and pollen? Or how about nasty smells and other gases like NOx or SOx? This article shows you what you need to know:

1. HEPA filters

HEPA filters are the most effective solution for capturing particles. “HEPA” sounds fancy, but it’s just a standard that means the filter catches 99.95% of particles .3 micrometers and above (they also get particles smaller than .3 micrometers–the .3 designation is based on the overlapping point of different types of filtering). That covers a lot of particulate pollution–the most-often cited figures are for 2.5 micrometers.


HEPA filters aren’t rocket science. They work pretty simply: particles get stuck in the synthetic fibers (using a few types of physical filtering processes). In fact, if you have a vacuum cleaner, it probably has a HEPA filter in it. You can get one for about $10.

Contrast that with the major purifier companies like IQ Air and Blue, which have proprietary HEPA filters with names like “HyperHEPA” that cost $200. These may have benefits like a longer lifetime, but direct comparison tests show the super expensive machines capturing no more particulate than the non-proprietary HEPA (1), even measuring down to .01 microns (2).

Conclusion: HEPA filters are great for capturing particulate pollution like viruses, pollen, dust, bacteria and more. If your concern is particulate air pollution, a HEPA filter is really all you need. And for that, you don’t need spend 8,000 RMB. You can make your own for 166 RMB.

Learn more: What are HEPA filters and how do they work »

2. Activated carbon filters

Activated carbon filters use charcoal screens to catch (adsorb) certain types of chemicals and organic matter that interact with carbon. For example, carbon will capture things like formaldehyde and other volatile organic compounds. But carbon will NOT capture particulate in general (see the extra test at the end of this article).

Learn more: Does activated carbon really work in filters »


Conclusion: Carbon filters can capture hazardous gases. They cannot capture particulate pollution like PM2.5 and pollen or pet allergens.

3. UV light filters

UV light filters are designed to kill bacteria and viruses. They work by shining a UV light (typically UV-C) on bacteria and viruses to kill or deactivate them. With that said, most UV-C lights take several seconds to kill viruses and bacteria, so may not be very effective in air purifiers because the air passes too quickly through the UV light. It’s also worth noting that UV light filters do not actually trap the pollution, only shining on it as it passes by, so they cannot help with other types of pollutants like pollen, dust, formaldehyde and other gases.

Learn more about UV Light air purifiers »


Conclusion: UV filters may kill viruses and bacteria, but they take time to do so.

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2 thoughts on “Overview: Types of Air Filters & What to Know”

  1. Great reading, whole blog, most appreciated thank you! If we go deeper, what do you think about quality of those impregnated carbon filters what are used as pre-filters for actual HEPA? Some ordinary e.g. Electrolux air purifier used in Europe market area use following pre-filter https://www.amazon.co.uk/Electrolux-EF109-Accessories-Purifier-Activated-Carbon-x/dp/B008PORWJ0 How is activated carbon attached to plastic (I think that it is not microglass fiber) filtration material? Can the activated carbon itself shed and cause pollution? Hard to find any kind of quality assurance and/or test document. Can the carbon itself contain some heavy metals and to what extent and so forth. What I found about activated carbon was that excessive amount inhaled might cause lung injuries ( https://www.ncbi.nlm.nih.gov/pubmed/16775697 and there are others). I think those are rare cases and well everything is poison only amount matters https://en.wikipedia.org/wiki/The_dose_makes_the_poison

    I suppose that due there is HEPA filter in my Electrolux machine AFTER activated carbon pre-filter this is assurance that nothing nasty should go in to room air, not any levels to make anything to worry about.

    • I’m glad you brought up the ‘foam’ carbon filters Miika! We haven’t done any rigorous tests on these yet, but it’s on our list of things to test! We did do some preliminary tests when we were looking at what carbon material we should use for our purifiers. When testing it then, we found that it wasn’t as effective as our regular granular carbon (the effectiveness was roughly 65% lower!). Based on that one test, we can make an assumption it’s not as effective, but more testing would need to be done to be sure.

      Most carbon material that’s sold have RoHS safety certificates validating that the carbon contains no harmful contents, so I wouldn’t worry about that too much. However the question of whether inhaling any particles ‘shed’ from the filter is probably not an issue. If this were to happen (again, it’s an if) it’s likely the material would get caught in the HEPA filter. Still, activated carbon is carbon after all, which is not as harmful to our bodies as heavy metals and other chemicals (as you say)


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