ROLLA, Mo. – The day before the federal government issued new recommendations that Americans wear cloth face coverings to help slow the spread of the coronavirus, a researcher at Missouri University of Science and Technology decided to test a few common household materials – pillowcases, scarves, furnace filters – “out of curiosity.” His early results, which he shared on Twitter Thursday (April 2), have attracted the interest of do-it-yourselfers, fellow engineers and scientists, and the general public.
The tweet also attracted the attention of a journalist from The New York Times, who reported on the project Sunday as part of the newspaper’s coronavirus coverage.
Dr. Yang Wang, assistant professor of environmental engineering at Missouri S&T, studies how fine particles like aerosols are transmitted. Recent research suggests that the coronavirus may survive on airborne aerosols for a few hours, although it also can be spread through larger respiratory droplets emitted through a cough or a sneeze.
After seeing posts on Twitter about whether scarves would sufficiently block aerosols, Wang decided to test a variety of household materials – including scarves, bandannas, pillowcases and household air filters – to see how well they might prevent the spread of aerosols.
Wang and his Ph.D. student, Weixing Hao, tested the various fabrics and materials using a scanning mobility particle sizer, which measures particle size and concentration. They then compared the “filtration efficiency” of multiple layers of each material against different aerosol particle sizes, ranging from a few nanometers to over 400 nanometers. Wang then shared their preliminary results on Twitter.
Wang and Hao found that the layers of scarves and bandannas did a poor job of filtering out aerosols. Pillowcase fabric fared somewhat better, depending on thread count. A 600-count pillowcase filters better than a 400-count one, the researchers determined.
But the best aerosol-blocking material of those Wang tested comes from commercially available household air filters. The multi-layered air filters work almost as well as n95 medical mask to block aerosols, especially smaller particles, according to Wang’s initial findings.
As more layers of filter materials are stacked, however, a change in air flow through the materials, or “pressure drop,” becomes larger. This pressure drop increase can make it more difficult to breathe. Wang and his team are also looking for a combination of materials that produces the highest filtration efficiency, but the lowest pressure drop.
This off-the-cuff study was more than just a passing curiosity for Wang, however. He is one of several Missouri S&T faculty, students and staff members who have come together to help local physicians and medical staff by providing masks and face shields. The effort began after officials with Phelps Health, a regional medical system based in Rolla, sought help from the university a couple of weeks ago. A handful of students have been working across campus to 3-D print masks and face shield brackets for the cause. The students have delivered hundreds of face shields to Phelps Health, but are still working on the masks.
To adequately protect health care workers, these reusable masks require some type of filter to block airborne particles that may spread the coronavirus or other diseases. That’s where Wang comes in.
Dr. Joel Burken, a fellow environmental engineer and chair of Missouri S&T’s civil, architectural and environmental engineering department, invited Wang to join the effort.
“We knew we had to come up with some sort of non-medical filters to use with these masks,” Burken says, “so I asked Yang to be a part of this campuswide project, and he’s been a strong team member.”
Wang and Hao are continuing to test different materials for the masks. While a furnace filter may be much more efficient at filtering out aerosols than, say, a bandanna, it’s possible that the components of such a filter could pose risks.
Different furnace filters are made of different materials, such as cotton, fiberglass or polyester. One further protective measure would be to wrap that filtration material with another type of material, such as a fabric.
“There are so many different types of fabric” to consider, says Wang, who recently won an international award for his research on aerosols. “Even for t-shirts, there are different types of materials. We plan to look at different types of pillowcases, bed sheets and other fabrics with different thread counts” as part of the testing, he adds.
Since posting his April 2 tweet, Wang has been surprised at the response.
“A lot of people are interested in this,” he says, adding that fellow academics have shared previous research that may help inform Wang’s current work.
“This is not a new field of study,” he says. “People in volcanic regions have studied the filtration qualities of various fabrics for years. I have received information about some of these studies. I find it all very helpful.”
Wow! America needs to read this information now.
It seems that we could mass produce some useful items now that are vital to our health.
Let’s do it- contact Bill Gates even to fund this.
Myself Mohit Sehgal from Punajb, India
I done my bachelor’s degree in Chemical engineering and now persuing my master in Environment Engineering.
Could metal filaments or metal coated fibers also used in the filter material. Viruses are not able to survive for long periods of time on some metals.
I wonder if Professor Wang could test the mask design found on diymask.site, which is a 2-layer mask design meant to house a filtration insert? The designer of the mask suggests using a paper towel, but I’m wondering what the filtration capability of this mask would be if it had a piece of Filtrete Healthy Living 1900 HVAC filter inserted between the layers.
What about vacuum cleaner filters and bags?
Any thoughts on the post about using the blue shop towels. Brand specificity mention was Zep industrial towels.
i dont suppose you could test Something like non woven fabric pet pads with and without a frabic exterieur , the kind you use for training dogs and cats. in carrying cages and at the vets They are lightwieght and capture droplets. Not sure if I am exlaining that well. They seem to made from the same material that hosptial bed drapes are made from, the non woven poly.
3M furnace filters are made of polypropylene and the 1900 model is rated for .3-1 micron. If sandwiched between two layers of cotton fabric ,is there any problem in using them for face masks? 3M Staes on their website that “they do not recommend altering their filters due to a lack of research”. If these filters are used to clean the air in your house wouldn’t the scaled down version to a mask also be safe?
Post this study for a peer review. Distributing a “study” like this during a pandemic without proper peer review is unethical. Using Twitter as a platform to spread this information without proper review is unethical
I am very interested in the results of filtration testing on materials for masks.
Many of my friends are sewing fabric masks; some designs include pockets to insert extra filter materials.
Some masks use fabric backed by fusible interfacing, thus 2 layers of interfacing plus 2 layers of fabric.
Additional filter materials (optional) include quilt batting (cotton, polyester, & blends are available), coffee filters, furnace filters, shop towels (synthetic), cotton towels, tshirts, etc.
As a quilter, I know that there are different fabric types, weaves, treatments, etc, even if you only test 100% cotton fabrics.
I am an alumnus of UMR in Ceramic Engineering.
Have you been able to test the safety of the Filtrete HVAC/furnace filters? The company has a standard Safety disclaimer for legal liability reasons since they have not been tested for this purpose but It would sure be great to know if, when placed between layers of fabric, they are safe?
Have you tested batik fabric?
I like to hear an update. I make my own face masks. I am not sure they are safe. My husband wears an N95 over and over again without changing it. It makes marks on his face that last for a hour after wear.
With respect !!!
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