
Low-cost measurement of facemask efficacy for filtering expelled droplets - pat2man
https://advances.sciencemag.org/content/early/2020/08/07/sciadv.abd3083
======
pat2man
The market for face masks is probably enormous right now but the information
out there on which ones to buy is anemic. I assumed this was because masks
were such a commodity that it didn't really matter which ones you bought, but
this article shows otherwise. Even just among the cotton ones there is quite a
difference.

~~~
techsupporter
I think the broader point is one that still stands: wearing _literally
anything_ over your nose and mouth is shown, by this study, to cut droplet by
at least 50%. Even the cotton varieties cut it from 70% to 90%. So...people
need to just slap something over their two air exchanging orifices on their
faces before leaving the house and contribute to the our greater health.

You're right about the differences in effectiveness but 70% is still pretty
good as long as many people are wearing something and _not_ exposing their
noses or wrapping the mask lovingly around their chins.

~~~
Kiro
You touch your face more when adjusting the mask so if it's not efficient
enough it may be a net negative.

Edit: This is one of the main reason the Scandinavian countries recommend
against _all_ mask use (including N95) so not sure why I'm getting downvoted
for merely saying an inefficient mask could have that problem.

~~~
aflag
I've seen that idea being tossed around, but are there any sort of studies
showing that the increased face touching can indeed make the virus spread more
than not wearing masks? It's a geniune question, I'd like to see studies
related to that.

For me, it's not really obvious that more face touching (even if that happens
in significant numbers across the population), causes the virus to spread more
than it would have without face masks. Reason being that it seems like spread
through surfaces is not as bad as through the air, so making the air cleaner
seems better than making the surfaces cleaner to me.

~~~
russholmes
I think the reason that various authorities advised against masks is political
- there simply weren't enough and to direct the supply to clinical workers.

~~~
throw_away
Which is damning in that they treated us like children who couldn't handle the
truth and were also so unimaginative that they did not consider alternative
face coverings.

~~~
russholmes
The government communication in the UK has been lamentable. Confusing,
inconsistent and patronising. On the other hand, we had idiots who stripped
the supermarket shelves of toilet rolls and canned tomatoes for months despite
being implored not to do so. If they had gone after the masks...

~~~
Johnjonjoan
Yes we should not have taken masks that would go to the NHS but don't forget
those masks should have been in government stockpiles well out of reach. How
can we blame and punish the publics self control (or lack of it) when it's a
government failure that caused the issue. Had we all bought masks and the
state made them instead of redundant hospitals perhaps we would be in a much
better place (less NHS casualties and physical/mental suffering).

All in all it just doesn't sit right with me to justify the government's
decision without mentioning they were the ones that put us in the position
where it had to be made.

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superkuh
Nice to see some empirical validation of valved N95 masks _still_ being better
than the vast majority of other "masks" when it comes to protecting other
people. And of course valved N95 masks are the gold standard for cheap masks
(not full organic vapor gas masks, etc) even outperforming non-valved N95 in
protection of self _because_ of the valve preventing them from becoming
unsealed during peak outflow. And of course they are much more comfortable to
wear for long periods and during heavy work.

I just wish the US government would go all in on production of real,
effective, fit N95 masks and distribute them to everyone.

~~~
yyyk
The authors themselves point out the valved N95 masks might be worse than what
the raw results show:

"Furthermore, the performance of the valved N95 mask is likely affected by the
exhalation valve, which opens for strong outwards airflow. While the valve
does not compromise the protection of the wearer, _it can decrease protection
of persons surrounding the wearer_." [emph. mine]

~~~
makomk
I'm pretty sure the difference they're referring to is already there in the
raw results - remember, they're measuring how well the masks protect others
against the wearer by filtering out expelled moisture droplets, and the
results show that valved N95 masks are worse than non-valved (though about as
good as the very best of the cotton masks).

~~~
yyyk
I doubt the results completely account for the airflow effect, and perhaps the
researchers were careful enough to note this.

After all, they merely tested one infected person speaking at whatever level
is normal for that person at that stage of the disease. It's quite possible
that the typical carrier has stronger flow. Besides, sometimes people yell -
quite a few people have reason to be on edge these days.

~~~
davidgould
They did not test an infected person. They measured droplets, not virus.
Disease progress is not relevant to this paper.

~~~
yyyk
Ouch. I read droplets and thought 'virus'. That said, my point about the
speaker not being representative is still correct. We have no idea if the
speaker's speech is typical. It could be their flow is lower than the average.

~~~
davidgould
They tested with four speakers and ran additional tests with one speaker.
Results are consistent across the speakers. Consider also that they are
measuring the relative filtration of different masks, not the absolute
filtration.

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jjoonathan
Yesterday I walked through a cloud of gnats with my mask on. I breathed in. No
gnats got through. That's something!

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carbocation
Somewhat off topic, but I think that the figure labeling in this article is
disappointing.

In figure 2, the masks are numbered but not named.

In figure 3, the masks are named but not numbered.

So, I can't (personally) tell which mask from figure 1 performed well and
which mask performed poorly.

~~~
Merrill
Table 1 gives the relation between mask names and numbers.

Having to use the table to relate the pictures to the results does seem very
poor.

~~~
carbocation
Thanks - I had actually missed that on my skim-through.

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mhb
Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth
Masks:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834/)

------
anonytrary
I have an even better way, albeit a bit dirty. Take a vape pen and simply put
your mask on before exhaling; "eyeball" the size and trajectories of the
exhaled vapor, select the mask that wins, and call it a day.

~~~
bjackman
I don't think there's any reason to assume vapour from a pen resembles the
droplets in your breath. In fact, that one of them is visible and the other is
not should suggest that they might behave very differently.

~~~
anonytrary
Mask hole size >> size of o2, n2, co2, and pretty much any aromatic molecule,
so I doubt it.

------
nabla9
The number of droplets is just one variable. Slowing down their speed is
another. Since droplets are heavy and fall down fast that dry aresols, just
having transparent face shield might give protection to others.

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jschwartzi
I’d be interested in seeing them test the CDC mask pattern for bandanas
because that pattern has you make like 9 layers. I slip a piece of shop towel
in the folds and put pipe cleaners at the nose bridge.

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082349872349872
The low-tech way I've seen (but not cross-calibrated), thanks to a pair of
argie firemen: use an aerosol spray can, eg hairspray, to see what makes it
through the mask candidate.

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rbritton
Have there been any studies that factor in the repeated reuse of the same
masks?

------
known
Check [https://masks4all.co](https://masks4all.co)

------
glofish
The damages and side effects of masks are consistently and systematically
downplayed. Benefits are vanishing if exist at all. The group think is such
that you will never see any of these mentioned in the media.

Here is a study that shows that cotton masks increase(!) the incidence of flu
like diseases:

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/)

And here is a study that warns that wearing masks leads to cardiac damage:

[https://link.springer.com/article/10.1007/s00392-020-01704-y](https://link.springer.com/article/10.1007/s00392-020-01704-y)

~~~
Nav_Panel
From first study: "The null hypothesis is that there is no difference between
medical masks and cloth masks. ... The control arm was ‘standard practice’,
which comprised mask use in a high proportion of participants [NOT "mask
free"]." \-- this means "increase relative to surgical masks", not relative to
no mask.

Second study is only N95s. Just don't wear an N95 if you need more air for
aerobic capacity. The OP study shows that they're not _that_ much better than
surgical masks anyway.

But hey believe what you want to believe.

~~~
glofish
not sure what your are getting at with the null hypothesis.

Look at the results. Mandatory cloth masks were associated with 3 times as
many ILIs (Influenza Like Illnesses). So it is not some tiny statistical
variation. It is a huge effect size.

As for the second study, it concludes:" _The observed mechanisms may lead to
more severe symptoms in individuals with impaired capacity for myocardial
compensation._ "

I am talking about how the all sources of information systematically downplay
the negative effects and serious side effects of masks.

Masks do have side effects. The relentless propaganda tells you that is a
"mere inconvenience".

~~~
Nav_Panel
> _3 times as many ILIs_

 _Compared to surgical masks_. There was no study of unmasked people. I expect
it would be 10x.

> _The observed mechanisms may lead to more severe symptoms in individuals
> with impaired capacity for myocardial compensation._

The study was only on N95 masks! Most people are wearing surgical or cloth,
it's irrelevant.

> _I am talking about how the all sources of information systematically
> downplay the negative effects and serious side effects of masks._

There appear to be very few, similar to how all sources downplay the negative
effects of walking on the sidewalk vs walking in the road.

I would be a lot more sympathetic if you targeted your ire at "washing down
surfaces", because that seems irrelevant with respect to spread. But _masks
work_ , and that's the long and short of it.

~~~
glofish
You should give the paper a more careful read, it discusses all that.

The control group was typical use, whatever the staff chose to do, which
included not using masks at all.

The use of masks in the control group was about 23%! And that included
medical, N95 and possibly cloth masks as well. Whatever they would typically
use.

Here is their conclusion:

" _Given the obligations to HCW (Healthcare Workers) occupational health and
safety, it is important to consider the potential risk of using cloth masks._
"

