Mask questions

[cos]

Considering only their effectiveness at a) slowing the spread of covid-19 and b) protecting you from covid-19, in public and grocery stores and similar (that is, I'm not asking about bacteria, fungus, healthcare settings, etc.)...

• If an N95 mask doesn't quite fit as tightly as it should, is it still significantly better than all surgical & cloth masks? Or does the imperfect make it likely not much better than a surgical mask?

• I've seen it claimed that multi-layer cloth masks are better than actual approved surgical masks. I'm very skeptical. But is there some validity to this claim?

• Is there any difference between US N95 masks and Chinese KN95 masks for this purpose? Other than the fact that I've never figured out how to actually fit a KN95 to my face :) But aside from the fit, are they effectively exactly the same thing (for this purpose)?

If you have helpful references or sources for answers to any of these questions, I'd like to read!

Comments

[wotw]

Re your final question, this was the first hit I got when I googled.

[blimix]

Disclaimer: All I have to offer is reasoning, not expertise.

Question 1: The finer the mask is, the more resistance it offers to air flow, and therefore, the more you will breathe around it rather than through it if it doesn't fit snugly. Therefore I would place less faith in a poorly fitting N95 than in any other mask that has reasonable effectiveness, regardless of fit.

Question 2: It will depend on the circumstances. For any given droplet size, the proportion of those droplets that make it through two layers of cloth mask should be about the square of the proportion that make it through one. So in a circumstance such as face-to-face conversation or being sneezed on, where the most likely vector of spreading is large droplets (which cloth masks intercept decently), added layers will have huge benefits. (They'll also slow down a cough or sneeze more, which will magnify this effect.) In a circumstance such as sharing indoor spaces for extended periods, where small airborne droplets are the primary danger, squaring a high proportion of those droplets passing through a cloth mask won't decrease the proportion that much. You'd be better off with a surgical mask.

Good luck with finding more educated answers and sources.

[macthud]

I highly recommend the "In The Bubble" podcast for accurate info on masks and other things. They have a maskmaker sponsor whose stuff sounds worth it, but I've been the beneficiary of a resident crafter's research and production, so I wear home-made multi-layer cloth masks.

From what I've garnered from various sources (sorry, no specific citations), most if not all "(K)N95" masks do not filter outflow -- so they don't help people nearby if you're infectious, but they do help you if people nearby are infectious. And of course, we don't yet have sufficiently fast, good, and cheap tests, so there's no way to tell whether you're infectious, so you should always wear something that helps protect the people around you.

Three-layer cloth masks, if made from the right materials, fit properly, etc., filter both inhale and exhale, so they help both you and people nearby.

Effectiveness if *everyone* is wearing three-layer masks with nominal 70% effectiveness is actually a *net* effectiveness of ~91% for everyone -- because it's 70% of your exhale + 70% of their inhale (which is an additional 21% of your exhale).

You in N95 and them in cloth gives *you* 70%+(95%*30%) = ~98% protection, and gives them only 70%.

Everyone in N95 gives everyone ~95%.

Surgical masks don't tend to fit very well, largely because they're mostly meant to protect the surgeon from the patient, not vice versa -- so exhalation venting around the sides is not considered problematic. Cloth masks *can* be made to fit quite well, and so both exhale and inhale can be fully filtered.

KN95 are generally considered not-quite-as-good-but-maybe because there's no supervision of the manufacture or materials nor assured testing of the product, unlike with N95. So, KN95 aren't *certain* to be shoddy, but as you've no doubt seen at various points, "cheap asian (not necessarily but often Chinese) knockoffs" of various things are *sometimes* just as good and *sometimes* not worth the air they displace and *on rare occasion* better than the original.

[cos]

> From what I've garnered from various sources (sorry, no specific citations), most if not all "(K)N95" masks do not filter outflow -- so they don't help people nearby if you're infectious, but they do help you if people nearby are infectious.

I know for absolutely sure that is not true, because I use N95 masks frequently these days. Yes, definitely, there are N95 masks that have outflow valves. That's a feature you can choose whether you want or not, when selecting a mask. For obvious reasons, N95 masks without valves are the ones being mostly sold currently.

[macthud]

Good to hear about the N95 valves' decreased ubiquity.

Among same material masks, better fit is better.

I don't know what effectiveness factor should be applied to compare worse fitting N95 against better fitting cloth or surgical...

[elusiveat]

My perspective is based on intuition and personal observation, not science.

On your first question, there are different ways of not fitting quite as tightly as it should. If you can get a good seal on the inhalation but some slight venting at the edges during exhalation, I think an N95 might still be worthwhile. As I understand it, the real selling point of the N95 is that it provides effective filtration of tiny particles on inhalation, and I haven't actually heard of anything else that does this.

On the other hand, if you're not getting a good seal on inhalation, I think a fabric mask with a better seal would be preferable.

One of my friends has spoken favorably of this product https://www.fixthemask.com/, which fits on over a mask to improve the seal, so that might be something worth looking into. The site shows it being worn over surgical masks but I think my friend was talking about using it with meltblown masks that are not N95s.