Homemade cloth masks should have at least two layers to help prevent the dispersal of viral droplets from the nose and mouth that are associated with the transmission of COVID-19, according to a study published online Thursday in the journal Thorax.
“A single-layer cloth face covering reduced the droplet spread, but a double-layer covering performed better,” the authors of the study write.
Still, “even a single-layer face covering is better than nothing,” they add.
These findings are in line with those from a study published earlier this month, which reported that a stitched, double-layered cotton mask was more effective at keeping respiratory droplets from reaching others than a single-layer bandana-style covering, a non-stitched mask made from folding up a cotton handkerchief, or a non-sterile cone-style mask available in most pharmacies.
The findings also come as more and more states and businesses are instituting mask requirements. On Saturday, a statewide mask mandate issued by Gov. Tim Walz will take effect. Minnesotans will be required to wear some kind of facial covering while indoors in business and public settings, including on public transportation.
Health officials at the Centers for Disease Control and Prevention (CDC) recommend that everyone over the age of 2 wear some form of cloth face covering in public settings to help keep COVID-19 respiratory droplets from reaching others.
How the study was done
For the current study, a team of Australian researchers compared the effectiveness of three type of facial coverings: a single-layer, “no-sew” covering made from a folded piece of cotton; a sewn double-layer mask (as described by the CDC); and a three-layer surgical mask. The two cloth coverings were made from medium-weight cotton with a 170-thread count.
In a laboratory, a healthy volunteer with no respiratory infections spoke, coughed and sneezed while wearing no mask and then while wearing each of the three types of masks. The researchers used a LED lighting system and a high-speed video camera to capture the dispersal of airborne droplets in each scenario.
The video recordings “confirmed that even speaking generates substantial droplets,” the researchers write in an article for the Conversation. “Coughing and sneezing (in that order) generate even more.”
The recordings also showed that the surgical mask was significantly better than the two cloth masks at reducing the spread of droplets in all three (speaking, coughing, sneezing) scenarios. The cloth masks provided some protection too, although the single-layered mask let more droplets through than the two-layered one.
“We do not know how this translates to infection risk, which will depend on how many asymptomatic or mildly symptomatic infected people are around,” the researchers write. “However, it shows a single layer is not as good a barrier as a double layer.”
“In practice, we don’t yet know which has a greater effect — wearing masks to prevent infected people spreading to others or protecting well people from inhaling infected aerosols,” they add. “Probably both are equally important.”
The researchers point to a recent CDC study involving two hair stylists who continued working while infected with COVID-19. (They were awaiting the results of tests.) None of the stylists’ 139 clients became infected. The stylists and the clients had all worn either cloth or surgical masks.
“This is reassuring evidence that infection risk is reduced when everyone wears masks,” the researchers write.
Practical implications
Cloth masks with more than two layers were not tested in the current study, but the researchers believe that, generally, “more layers are better.” They point to a study that suggests a 12-layer cotton mask may be about as protective as a surgical mask.
Of course, stitching together 12 layers of cotton is not a practical thing to do. The study’s authors do have some other suggestions, however, for how you can make your cloth masks more effective:
- Increase the number of layers (at least three layers).
- Use a water-resistant fabric for the outer layer.
- Choose fabric with a high thread count (so a tighter weave, for instance from a good quality sheet is generally better than a fabric with a looser weave that you can clearly see light through).
- Hybrid fabrics such as cotton-silk, cotton-chiffon, or cotton-flannel may be good choices because they provide better filtration and are more comfortable to wear.
- Make sure your mask fits and seals well around your face.
- Wash your mask daily after using it.
FMI: You’ll find the study on the website for Thorax. You can find step-by-step instructions on how to make a cloth mask on the CDC’s website.
OMG, I’m sure this will provoke tirades by the anti-mask nihilist right and we will be treated to determined assertions that the laws of physics categorically prove that two layers simply cannot be better than one! Indeed, two are worse than one!
But as Star Trek’s Commander Montgomery Scott famously declared: “I canna change the laws of physics! I’ve got to have [two layers]!”
And yet, here is another brand new (June 2020), peer reviewed CDC study of 10 RTC’s (Randomized Controlled Trial ) that concludes:
“Disposable medical masks (also known as surgical masks) are loose-fitting devices that were designed to be worn by medical personnel to protect accidental contamination of patient wounds, and to protect the wearer against splashes or sprays of bodily fluids (36). There is limited evidence for their effectiveness in preventing influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure. Our systematic review found no significant effect of face masks on transmission of laboratory-confirmed influenza.”
https://wwwnc.cdc.gov/eid/article/26/8/20-1498_article
Yet, incredibly, despite your definitive proof (relating to the common flu), some “conservative” Repub governors are (right now!) mandating masks, apparently to help prevent Covid spread[!?], and even Freedom Fighter Trumpolini himself urged folks to wear one (this week)! How could this possibly be in the face of your irrefutable evidence? This does not compute!
Perhaps the following will shed some light? CDC, June 28, 2020: “Wearing a cloth face covering will help protect people around you, including those at higher risk of severe illness from Covid-19…The spread of Covid can be reduced when cloth face coverings are used with other preventative measures…”
Seems pretty straightforward (for those who want to understand and not misinform–as though this Trump-caused catastrophe is all a funny little game…)
BK, your argument amounts to pointing out some GOP politicians are not above playing the same game Democrat politicians play. First of all, that certainly isn’t news to me, and secondly, it does absolutely nothing to rebut my position.
To quote protest signs I’ve seen online; do better.
Yes indeed. You are the voice of reason in a sea of irrationality and scientific illiterates! Failed Dems to the left of you, failed Repubs to the right!
Soldier on….
Curris, why do you want businesses to fail? Why do you want to destroy the economy? Why do you want people to lose their jobs?
Much of the rest of the world is beating Covid because they are using masks and social distancing. Yet you and others like you seem determined to make this country fail because you won’t take these simple steps. Why? I don’t get it.
And let’s not forget that this is the response of “conservatives” to being told to shoulder an (extremely minor) inconvenience, decrying the mask mandate as “tyranny”.
Methinks they have no real idea of tyranny, although they are delighted to reside in a “democracy” that allows an unqualified, obviously mentally unbalanced ignoramus to lose a national election by millions and millions of votes yet still take office–as long as he was the candidate of THEIR (minority) “conservative” faction. But a Dem governor winning a solid majority and exercising statutory emergency powers is a “tyrant”. Can one imagine what would happen if a (popular vote-majority) Dem president demanded that “conservatives” undertake an ACTUAL sacrifice for the nation? They go crazy with rage and indignation over being told to wear a mask in the liquor store! Even teenagers are more reasonable…
I gotta give you credit, Curtis. You’re making an awfully good case for more social distancing.
lol. That’s ironic, although not intentional on your part.
Between you and I Brian, there is at least one moderator that is doing yeoman’s work in keeping my opinions distanced from y’all, if not my person.
“Limited evidence” is not the standard science uses to advance a proof.
It’s only a guess on my part, but that guess is that the number of layers of fabric in a mask makes no difference whatsoever if that mask only covers someone’s mouth and not their nose. I saw (at a safe distance) plenty of people on this morning’s errands (post office, Cub) who were “wearing” masks, but had pulled the masks down so that their noses were not covered. I also encountered a few whose idea of “wearing” a mask seemed to be to wrap the loops around their ears, then tuck the entire mask up against their Adam’s Apple under their chin. Doing so exemplifies “pointless.”
It’s probably scant comfort here, but Section 3a of Governor Walz’s executive order on mask wearing reads “A ‘face covering’ must be worn to cover the nose and mouth completely”.
I doubt any of those you saw took the time to read the executive order, however (nor bother to listen to or read the details of the widely available coverage of how it is to be adhered to).
If anyone here is interested, the entire text of the executive order can be found at:
https://www.leg.state.mn.us/archive/execorders/20-81.pdf
The more layers the better?
“Of course, stitching together 12 layers of cotton is not a practical thing to do.”
Nor is trying to breathe through them! I don’t believe I have seen ANY recommendations for a 12 layer mask anywhere. Quite to the contrary, the articles I’ve read emphasize that breathability has to be considered as an important component in selecting a suitable and effective mask construction. To put it bluntly, if people can’t breathe through a mask, they won’t wear that mask.
And even if a person were to attempt to utilize that theoretical 12-layer mask, the fact that the air cannot pass through it would mean it is going to be forced out around the edges, rendering moot any filtering effectiveness of the mask layers, regardless of how many layers there are.
The more layers the better? I think the authors forgot to consider the law of diminishing returns!