Great article by @zeynep and @jeremyphoward. To answer the question they get asked what and "where to buy proper masks," below is a thread. I have no financial interest in these recommendations. My family uses this near N95 solution that costs 17-60 cents/day.
I'll tell you what to do and then I'll explain why and provide the evidence.

You need a good quality surgical mask plus a mask fitter like the one made by @FixTheMask.

A disposable face mask made out of meltblown polypropylene layer that passes the candle test is likely good. Image
Those candle grade ones appear to cost 17 cents each on Amazon. Personally I prefer to buy ASTM Level 2 or 3 certified masks. Those run 40 to 60 cents. I prefer the Ambrust, which @FixTheMask found in their testing to offer the best filtration and

decent breathability. My essential worker son wears this combo every day, all day. Testing of some masks here.
fixthemask.medium.com/surgical-mask-…
Now on the mask brace or mask fitter (same thing). IMHO, the @FixTheMask one is a no-brainer to buy. It's the best one and right now there are only two you can buy. Here's a 3-minute video of why you should do this and why it works.
The mask brace is reusable and costs about $15. FixTheMask.com and folks at the University of Wisconsin show how you can make a DIY version. making.engr.wisc.edu/mask-fitter/
But if I were you, just buy a @FixTheMask brace or a premade Badger Seal. I've not tried the latter, but both work well to protect you. The FixTheMask one looks better to me. The premade versions are so cheap why bother making one?
Let me also add that the Zubrex tested well by FixTheMask and costs 26 cents each. So if you're on a tight budget, that seems like the best value with quality assurance.
Now the evidence. @zeynep and @jeremyphoward linked to an U of Iowa paper. But another impressive one came out last week. “Strategies to minimize SARSCoV2 transmission -- combined impacts of ventilation and mask effective filtration efficiency.”
medrxiv.org/content/10.110… Image
Their findings are astonishing. They tested, using manikins, a room of socially distanced students and a teacher in a typical classroom. In one test, all occupants used typical cloth masks. Image
Then they did another test. They placed a mask fitter/brace plus a surgical mask on all the occupants. The combination of the fitter plus surgical mask reduced the transmission risk of infection by a factor of over 100 compared to typical cloth masks!
Here is the key take away: Conditional indoor infection probabilities as low as <0.0001 (0.01%) per hour might be reached with the use of surgical masks and mask fitters alone. No other swiss cheese interventions. Alone!! Obviously ventilation helps too.
From p. 67 of the preprint: With the use of a mask fitter, one can achieve an effective filtration efficiency approaching the material filtration efficiency for a mask.
Preprint's p. 66: Inexpensive disposable masks used with a mask fitter can achieve approximately 95% effective filtration efficiency in some cases.
From p. 65:

3. Leakage rates around masks are typically in the range of 20-80% when fit reasonably well to the user’s face, resulting in effective filtration efficiencies that are much lower than the material filtration efficiency.
4. With the use of a mask fitter, one can achieve an effective filtration efficiency approaching the material filtration efficiency for a mask. Inexpensive disposable masks used with a mask fitter can achieve approximately 95% effective filtration efficiency in some cases.
The beauty of this solution is we have it NOW. It can scale NOW. Surgical masks are easy to make at scale compared to N95s, which require specialized equipment.
If you don't want to read the whole paper, this thread has more.
Unfortunately, all the engineers who wrote the paper are not on Twitter, so none of the aerosol scientists IAQ experts on Twitter have tweeted it out yet. @linseymarr
@ShellyMBoulder
@jljcolorado
@Poppendieck
@ProfCharlesHaas
@kprather88
@PrasadKasibhat1
@Don_Milton
@vfmcneill
Again, I have no financial interest in these recommendations and have never met anyone at the recommended companies either. This is based on my own research. Stay safe!

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More from @DavidLKeating

15 Jan
This new mask to prevent #COVID19 is on the market. If you need solid comfortable protection, it seems like a solid product. I've not bought one yet. They are going for NIOSH approval as a respirator and I'll think they'll get it.
openstandardindustries.com
I looked at their test results. It seems like the best you can get.

Watch this video to learn more about the story of how it came into being.
The only uncertainty I have is how well people can hear you when you have it on. I think it is better than most reusable masks.

So it is probably best for essential workers who don't have to do a lot of talking. So not great for a teacher, for example.
Read 4 tweets
6 Jan
1/ Must read new preprint: Strategies to minimize #SARSCoV2 #COVIDisAirborne transmission -- combined impacts of ventilation and mask effective filtration efficiency. medrxiv.org/content/10.110…

Extensive set up of manikins and analysis of indoor classroom.
2/ Key take away @zeynep @ScottGottliebMD @DrTomFrieden @EricTopol @DrEricDing @ASlavitt: we can all upgrade our masks cheaply. Conditional indoor infection probabilities as low as <0.0001 (0.01%) per hour might be reached with the use of surgical masks and mask fitters alone. Image
3/ @FixTheMask makes a cheap reusable mask fitter. I use it, it's great. UW invented a DYI Badger fitter. making.engr.wisc.edu/mask-fitter/ but @FixTheMask one tested better. N95-like protection for 26-50 cents per use.
Read 25 tweets
11 Dec 20
@linseymarr @MonicaGandhi9 I have to say this is really frustrating to read this. People are still scrambling to figure out mask hacks. STOP!😀

The BEST and CHEAPEST protection for the average person is a Level 2 or 3 certified surgical mask with the @FixTheMask brace. It's better than an N95
@linseymarr @MonicaGandhi9 @FixTheMask for most people because the fit is a no brainer. And it is MUCH more comfortable than all the hacks.

Data:
fixthemask.medium.com/fix-the-mask-d…
@linseymarr @MonicaGandhi9 @FixTheMask When I wear the @FixTheMask brace, the fit is fantastic. Way better than futzing with an N95. Look at how simple!

Read 5 tweets
18 Sep 20
1/25 @Gladwell did a brilliant interview podcast with @michaelmina_lab. One of the questions @Gladwell asked is why don’t we have the #dailyrapidtest already to fight #covid? The answer is the FDA. Here is a lightly edited transcript of that part of the podcast.
2/ The rapid tests for #covid look like a pregnancy test, and they work like a pregnancy test actually. It's a little piece of paper, generally speaking.
3/ And you put some of the sample, whether that is a swab that's been mixed with some saline solution, or saliva onto a paper strip, and... and it shows up with line. It turns either, for example, red if it's positive or blue if it's negative.
Read 26 tweets

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