The type of mask matters

I haven’t seen this brought up here, so wanted to make everyone aware of something i read form the team at the University of Minnesota:

The whole thing boils down to a fairly simple graphic:

With all of us planning to meet with our teams more often and for longer hours over the next few weeks, be aware that the type of mask you use matters! A simple evening meeting during the week may last 3 hours or so. A weekend meeting may last 8. Be aware of how effective your masks are over this timeframe!

While we can’t all go through professional fit testing, the goal is pretty straight forward - ensure the mask gives you a full seal all the way around. No gaps, no outlet for air other than through the fabric of the mask. And that’s the problem with most other types of masks - they bunch up on the sides, leaving plenty of unfiltered outlet (thus the “% outward leaking” number provided in the graphic!).


I’d take these numbers with a grain of salt. Especially considering Omicron is likely at least twice as contagious as Delta. I’d bet that those exposure numbers are likely greatly inflated compared to the reality we face today.

With that said, the premise of the article is still relevant in that better mask = more protection.


I’d also like to emphasize:

By nature of this being a two-dimension table, my mask protects you, and your mask protects me. This is NOT a personal decision, it is a collective one.


You are of course correct that those times are probably much lower with Omicron, but the relative protections are almost certainly similar. A well fit N95 or better will give you significantly more protection than a cloth mask.


another graphic of the same:

Means no facial hair (you need to be clean shaven), and the mask is going to necessarily press into your face and nose. It also means don’t constantly fidget / touch / adjust.

And N95 are regulated by NIOSH, KF94 are regulated by South Korea, KN95 are not regulated by anyone (and should be assumed to be junk).

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I will note that the symmetrical nature of the graph is a bit suspect. My understanding is that the person who has Covid wearing a mask will yield much more protection, but both people wearing one is even better. Particularly when you get to the respirator level, wearing one of those is able to provide more bidirectional protection.

This is an old but somewhat apt and simplified version.

Now imagine in the same analogy a respirator like an N-95, KF-94 or KN-95 (from a reputable supplier) are like pants made of raincoat materials. This will provide even more protection, but ultimately the more people who are masked up the better, especially with asymptomatic spread you may not know who’s carrying it.

Be especially mindful that you may not know who on your team has underlying health risks, or whether they live with imunocompromised individuals, so even if your school or organization can’t require masks, please be considerate of eachother and everyone’s safety. I know I’ve been wearing BOTN KF-94s for a while now and find them to be fairly comfortable. The supply chains a bit all over the place right now, so proper mask management is even more important. Each is rated for 40 hours of use, so if you let them air out in paper bags between uses respirators can get you a long way.


I might add proper ventilation (air exchanges per hour) or mechanical filtration via HEPA filters or portable air purifiers will substantially increase these times, described here. A few box fans and some 12 MERV filters will go a long way to extend those estimates if you didn’t want to buy HEPA or ULPA filters from McMaster.

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While they don’t meet certain US standards, it’s also noted than many are still more effective than cloth masks.


“KN95 masks that don’t meet U.S. regulatory standards still generally provide more respiratory protection than surgical or cloth masks and can be used in certain clinical settings,” said Michael Argentieri, vice president for technology and safety at ECRI. “Hospitals and staff who treat suspected COVID-19 patients should be aware that imported masks may not meet current U.S. regulatory standards despite marketing that says otherwise.”

While not providing 95 percent protection, ECRI researchers say many non-certified masks that have head and neck straps, as opposed to masks with ear loops, better conform to and seal against the wearer’s face, ensuring that air being breathed is filtered.


This bit isn’t terribly scientific:
Here in the US it seems a lot easier to find masks at least claiming to be KN95’s, so I’d be unsurprised if you’re more likely to find non-compliant ones.

This bit is more scientific but with caveats:
The CDC/NIOSH have filtration testing data for KN95’s,KF94’s,etc. here:

Caveats: Sample sizes (10 units) are not terribly large, many SKU’s have not been recently tested, and only filtration material (not fit) is evaluated.

Photo from evaluation of “Dr. Puri” KF94 Mask:

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Did you read your own source?
“NIOSH has been informed that many legitimate manufacturers in China have been counterfeited. In such cases, NIOSH has no way of verifying which products are counterfeit and which are authentic. While the manufacturer listed in the table is shown as the manufacturer of the product evaluated, NIOSH has been informed that some of these are actually counterfeit products. Some products with legitimate manufacturer names, showing poor filter penetration results (<95%), are counterfeit products. A number of manufacturers have also informed NIOSH that they did not produce the products associated with their name. NIOSH urges purchasers of masks and respirators that may have questions about the authenticity of these products to contact directly the manufacturers and others in the supply chain as needed to verify that they are obtaining legitimate products.”

keep this impending argument civil… please

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I did take note of this too when I first saw the symmetric graphic. But I didn’t worry too much about it given the overall sentiment of “better mask better, especially w/ more contagious variants”. It does seem intuitively the closer you can stop (or slow) transmission to the source the better. but that model may fall apart at some point. I am no expert.

Yes, yes I did. Just so we’re clear here, I’m not trying to attack you personally nor attack your conclusion. With sensitive and technical topics like this, I just prefer to at least present some sources, data, etc. I’ve used to come to my conclusions.

You seem to be suggesting I have an opinion or notion and simply googled some source without reading it. I debated on whether or not to plaster all of the disclaimers and caveats in the link (the one you linked is just one of many), but decided against it for brevity. I’ll admit that may have been a poor trade-off decision, but I figured folks were more likely to visit the link at all if the post were more brief than not.

I’m not a medical worker, but my job requires me to come to office anywhere between once to all days in a working week so I wanted better fitment and/or protection than surgical style masks. Given that legit NIOSH-approved N95 masks were both expensive and better off being used by front-line workers (especially earlier in the pandemic), I have personally been using the NIOSH/CDC data for international masks to identify potential masks for personal and professional use. After identifying promising candidates, I try to find non-Amazon sources that appear legit and test for fit. Amazon has historically battled with counterfeits for “everything from laundry detergent to running shoes” and for these masks I’m generally unwilling to take my chances if I can help it.

Based on the test data and personal fit, my wife and I have settled on using Powecom KN95 masks from Bonafide Masks, a distributor in New York state for whatever that’s worth. As an example, we have also tried the Dr. Puri KF94 masks, but found they did not fit me particularly well (Medium was too small and Large was too big, classic Goldilocks problem). Data for both masks are below. To reiterate, there are many caveats to the data. (Edit: And as you noted, it is quite possible to get a counterfeit version of any of the masks tested)

I think given the data and the absurd amount of masks available online claiming to be KN95’s, you might be better off just trying to find a legit KF94 mask instead. I think it’s worth noting that while looking for KF94 instead of KN95 likely reduces the size of your search space, there’s still a chance that you’ll get a non-compliant/counterfeit mask.

Powecom KN95 Test Data:

Dr Puri KF94 Test Data:

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Now I’m not saying that chart is “bad” but from a critical standpoint seems incomplete. This is just going off everything we’ve heard before and the “Pee Test” is a good visual.

If we’re standing 6 ft apart with no masks and I’m a jerk so I sneeze in your direction, you’re going to feel it because I can project it your way immediately.
Same scenario, but now instead of me sneezing, you inhale as hard as you can because you’re weird and you want to smell my breath. Not gunna happen.

Now here is what’s bugging me. What is the scenario they’re using that says only you wearing a mask is just as effective as only me wearing a mask. I’ve always worn a cloth mask under the assumption that I’m protecting my coworkers and getting nil benefit myself. (as we’ve been told in the past for anything less than N95)

And the point I want to emphasize. It’s the wild west in the KN95 space. Pretty much anyone can produce a good looking mask with inferior materials that provide no filtering, slap a KN95 label on it and sell it to the public with zero repercussions. And unless you have the means to test what you’ve bought, your mask (from the NIOSH data) could have as wide of a range from 98.65 to 5.3% effective (Dongguan HuaGang Communication Technology Co., Ltd. as the example)

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