One of the most commonly used masks/recommended to protect against COVID-19 is N95.

Is there any upside of using N95 masks instead of N99 or N100 to protect against COVID-19?

N95 which filter 95% of particulates, while N99 or N100 filter 99% and 99.97%, respectively.

For example:

Health officials recommend medical staff wear so-called N95 masks because they filter out about 95% of all liquid or airborne particles.

The N95 equivalent in Europe is FFP2, the N99/100 equivalent in Europe is FFP3, and the N95 equivalent in South Korea is KF94.

Prior research:


Infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Health that the N95 is still the recommended face mask for health professionals, because it has the capacity to filter out very small particles that could possibly contain the virus. “This is different than a surgical mask, which can only stop larger droplets,” says Dr. Adalja.


In the United States, respirators must meet NIOSH (National Institute for Occupational Safety and Health) standards. Within this standard, there are several classes of respirators depending on the degree of oil resistance:

Class N: no oil resistance. A distinction is made between N95, N99 and N100. The number after the letter indicates the percentage of filtration of suspended particles


When worn correctly, N95 respirators block out at least 95% of small airborne particles. So the respirators can filter out some droplets carrying coronavirus. The coronavirus itself measures between .05 and 0.2 microns in diameter, according to a recent article in The Lancet.

I have cross-posted the question at:

  • 2
    You mean like that it will be (most probably) easier to breathe in N95 (can test it on 3M filters, if that is of interest)?
    – P Marecki
    Commented Mar 23, 2020 at 1:39
  • @PMarecki thanks, yes that sounds like an upside Commented Mar 23, 2020 at 2:03
  • Lacks prior research, which is surprising for you, Franck. And it's irrelevant where else you posted it off site.
    – Carey Gregory
    Commented Mar 23, 2020 at 4:08
  • 1
    @CareyGregory I think where else I posted the question is relevant so that answerers are aware of other anwers. I did some prior research: shall I list the web pages that I found that do not answer the question? Commented Mar 23, 2020 at 7:15
  • 1
    You'll sweat less. N99 and above have all-around rubber seals in my experience. N95 might not even one on the nose (but the good ones to have one there). Since this is personal experience rather any studies, I'm not putting it as an answer. Commented Mar 23, 2020 at 19:14

2 Answers 2


Yes, there are several "upsides" as you put it.

  • It's cheaper
  • It's easier to breath in
  • It's sufficient for catching particles smaller than it's actually designed for...

Now, that last point is what's important. According to 3M's own documentes on various types of filters and masks, it seem that there's an electrostatic effect between the layers of the filters and the particles hitting it. So:

  1. filter "grid" does not have to be smaller than the particles themselves
  2. Apparently because of the electrostatic effects, particles are attracted to - and prefer to stick to, the fibers of the filter.

From [2]:

Because of the various mechanisms by which particulate filtration occurs, the smallest particles are typically not the most difficult to filter. Most particulate filters have a region of lower filtration efficiency somewhere between 0.05-0.5 μm.1 Particles in this range are large enough to be less effectively pushed around by diffusion, but small enough to be less effectively captured by interception or impaction. The most penetrating particle size (MPPS) will depend on the filter media, air flow, and electrostatic charge on the particle. Filters that use electrostatic attraction may have a MPPS shifted to a slightly smaller size range.

enter image description here

Appendix A (equivalent mask standards) 1

  • N95 (United States NIOSH-42CFR84)
  • FFP2 (Europe EN 149-2001)
  • KN95 (China GB2626-2006)
  • P2 (Australia/New Zealand AS/NZA 1716:2012)
  • Korea 1st class (Korea KMOEL - 2017-64)
  • DS (Japan JMHLW-Notification 214, 2018)

Appendix B (Classiifcations) [2]

Standard            Classification      Filter Efficiency
NIOSH 42 CFR 84     N95                 ≥ 95%
NIOSH 42 CFR 84     N99                 ≥ 99%
NIOSH 42 CFR 84     N100                ≥ 99.97%
EN 149:2001     FFP1 (filtering facepiece)  ≥ 80%
EN 149:2001     FFP2 (filtering facepiece)  ≥ 94%
EN 149:2001     FFP3 (filtering facepiece)  ≥ 99%
EN 143:2000, EN 140:1999, EN136:1998    P1 (elastomeric facepiece)  ≥ 80%
EN 143:2000, EN 140:1999, EN136:1998    P2 (elastomeric facepiece)  ≥ 94%
EN 143:2000, EN 140:1999, EN136:1998    P3 (elastomeric facepiece)  ≥ 99.95%
GB2626-2006     KN/KP90                 ≥ 90%
GB2626-2006     KN/KP95                 ≥ 95%
GB2626-2006     KN/KP100                ≥ 99.97%


  • A problem with this answer is that COVID-19 is now understood to be airborne, resulting in much smaller particles than shown in the graph. Even in 2020, it was thought that not only sneezes spread the virus, but breathing, talking, etc. "The size of the particles generated from these [flu] patients ranged from <0.1 μm to 10 μm. A significant number of particles <1 μm in size were generated by the coughing patients." ncbi.nlm.nih.gov/pmc/articles/PMC7579175 Also see: nature.com/articles/d41586-022-00925-7 Commented Oct 20, 2022 at 14:41
  • @glenviewjeff I think you might have misunderstood the question/answer. COV size (diameter) ranges between 60 to 140 nm (0.06 - 0.14 um), so FFP2 is generally considered sufficient (min 95% filtering efficiency), because of the above reasons. Of course it is also a matter of personal opinion of what you consider sufficient, ie. what risk you are willing to take. See this answer. Note N100 (and alikes) provide better/stronger/more narrow filtering.
    – not2qubit
    Commented Oct 21, 2022 at 11:37
  • I believe there may be multiple layers of misunderstanding. First, it seems I was confused when I wrote that the particles are smaller than in the graph. I have seen this graph used to claim that N95s trap more than 95% of the coronavirus. However, the graph shows that if the infectious particles are between about 50 and 110 nm, an average N95 will allow in about 5% of the particles. This is exactly as designed, not better than designed. Commented Nov 13, 2022 at 13:56
  • 1
    That having been said, in a 2020 interview, a professor specializing in airborne virus transmission said that the virus attaches to water droplets or aerosols (i.e. really small droplets) that are generated by breathing, talking, coughing, etc. "Breathing and talking generate particles around 1 micron in size, which will be collected by N95 respirator filters with very high efficiency." [This is corroborated by the sneeze particle distribution on the right of the graph.] Commented Nov 13, 2022 at 13:59

As the other answerer said, the functional difference (for airborne virus) in filtration is low between N95, N99, and N100. However, it should be noted that fit and leakage is very important. If there are gaps, even small gaps.

Fit testing is part of the NIOSH standard. Google QLFT and QNFT. I'm not sure about other standards, which might just be about the filter. (I assume if they are respirator standards, then there is also a fit test).

Proper usage of / protection with N95 masks requires a good seal. Based on talking to some nurses, N95 fit testing in hospitals (in the USA) isn't that prevalent or well known.

If you want to run a very cheap variant of the QLFT fit test, take a look at this video (I made it, but has references) that mimics the QLFT.

I also touch on PAPRs / Viral Helmets here (also my site) and opine that N95 or KN95 is usually sufficient for most cases if you have good fit. I don't go through the underlying modeling, but that is based on the Jimenez model

  • 1
    The functional filtration difference between N100/P100 masks is that they filter out 99.97% of the 300 nm particles. This is 167-fold greater filtration than N95 masks that only filter out 95% of these same particles.
    – polcott
    Commented Oct 9, 2021 at 19:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.