I made a new, easier design that doesn't require any sewing and is less embarrassing. I don't know how to upload pictures but this is the video of how to do it. https://www.facebook.com/buzzyhelps/videos/338485333774268/
Inexpensive double-thickness cloth masks are widely used in Southeast Asia, and the research on these varies. The original question was how well the barriers protect bystanders when the wearer coughs or sneezes. Surgical masks are a courtesy to others, not a personal protection, so how well do they hold up in this situation?
First, what's in a sneeze? The mode of transmission of high-attack rate fast-moving epidemics has been determined to be from inspirable respiratory droplets, with a diameter in the range 10–100 µm. (1) The research studies looking at transmission have been done studying influenza, but the COVID19 mechanism of spread is also felt to be primary respiratory, not aerosolized droplets. OK, then.
In a lovely “let’s have sick people cough on a plate”(2) study, both surgical masks and N95 masks stopped influenza from infecting a petri dish at 20cm, compared to 100% infection with no mask. Doesn’t answer the cloth question, but does seem to indicate that SOME barrier works better than nothing. Another study looked at surgical masks versus none in household contacts, but since ⅓ of the control group couldn’t help themselves and wore homemade masks anyway, the wishy-washy non-statistically significant “masks seemed to reduce household infection” didn’t add much to the literature. (When they analyzed surgical or homemade mask v. no mask, however, the masks DID make a significant difference!) (3)
The other question is protection of the wearer. This is moderately better researched, and arguably more important. Documenting the worst outcome, one study looked at the filtering capacity for particulate matter of 10 μm or less (PM10), and found four cloth masks ranged from 63% to 84%. (4) Mind you - we care most about a diameter OVER 10 μm, but still, these masks filtered better than nothing at the smaller end of the spectrum. Every single other study gave better results for any barrier, with few finding clinical differences between surgical and N95.(5) In addition to the multiple studies finding no statistical differences between N95 and surgical masks for healthcare workers, several point out that handwashing is so important it can’t be ignored. On my YouTube post someone posted a link of one huge, beautiful study that could have kaboshed the bra: 569 healthcare workers with reused cloth masks had an almost double relatively increased risk - 1.72x (95%CI1.01 to 2.94) - of having a laboratory-confirmed viral infection than the 580 with medical masks. I posted a “doubled-up bandana doesn’t work” mea culpa, then started reading the fine print: The cloth group only handwashed 11 times a day, compared to 14 by the medical group, p<.0001. (6) Confound it, as we'd say!
So what have we learned? First, that there aren’t a lot of studies about whether you can protect your loved ones by wearing a mask. Second, there are NO studies with a padded cloth DIY mask. Go figure. Third, though, any barrier was better than none in protecting petri dishes, and a mix of surgical or cloth did protect household contacts better than the INTENT to wear a mask.
For protecting yourself as a healthcare worker, wetting bandanas didn't make them better, and 3 ply was better than 2 ply cotton that had been washed. Fortunately for those who are stuck with a surgical mask instead of an N95, most studies did NOT find a huge difference in infection. While the bra-wearing healthcare worker was never the question, the jury is still out. However, if you're working with sick people the jury is DEFINITELY in: Wash your hands.
PS: The testing companies cost $2500 and need 46 samples. If you are a bra manufacturer interested in letting us pay to test the bras, we’d be MOST interested in 23 identical padded C cups, please. 1. Stilianakis Y, Dynamics of infectious disease transmission by inhalable respiratory droplets J R Soc Interface. 2010 Sep 6; 7(50): 1355–1366. 2. Johnson DF1, Druce JD, Birch C, Grayson ML. A quantitative assessment of the efficacy of surgical and N95 masks to filter influenza virus in patients with acute influenza infection. Clin Infect Dis. 2009 Jul 15;49(2):275-7. 3. MacIntyre CR Cluster randomised controlled trial to examine medical mask use as source control for people with respiratory illness. BMJ Open. 2016 Dec 30;6(12):e012330. 4. Neupane BB Optical microscopic study of surface morphology and filtering efficiency of face masks. PeerJ. 2019 Jun 26;7:e7142. 5. Cowling BJ. Face masks to prevent transmission of influenza virus: a systematic review Epidemiol. Infect. (2010), 138, 449–456. 6. C Raina MacIntyre et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workersBMJ Open. 2015; 5(4): e006577.