Wearing a face mask in public is now the new normal. Many countries have made face masks mandatory when venturing outside of one’s home, and some US states (New York, Pennsylvania) have done the same. Even if you live in a state that hasn’t enacted a compulsory mask policy, it’s still probably a good idea to have one handy when traveling to a crowded place.
Of course, N95 and surgical masks should be saved for the health care workers battling this pandemic on the front lines. So, many people have been constructing DIY face masks for themselves. But what are the best materials to use when making your mask?
A new study just released by the American Chemical Society delved into this question and found that a combination of cotton with chiffon is the best combination to block out viral aerosol particles. Chiffon, for those unaware, is a lightweight semi-transparent fabric often used for nightgowns.
SARS-CoV-2, the coronavirus that causes COVID-19, is primarily spread via respiratory droplets. These droplets enter the air anytime infected individuals cough, sneeze, speak, or breathe. Now, these droplets can range a bit in their size, and the smallest of droplets are capable of passing through some cloth fibers. With this in mind, many experts and pundits alike have questioned if cloth masks are effective at mitigating the spread of the virus.
To end the debate once and for all, Supratik Guha from the University of Chicago and his team decided to test a variety of fabrics, both singularly and in combination with other materials, to see which filtered out aerosols most effectively.
A device called an aerosol mixing chamber was used to create various particles of different sizes (anywhere from 10 nanometers to 6 micrometers across). Then, a fan was used to blow the aerosol particles into the fabric samples. Researchers were even able to mimic the airflow rate of a resting individual’s breathing patterns.
Among all the tested fabrics and combinations, one combo was particularly effective. One layer of a tightly woven cotton sheet mixed with two layers of polyester-spandex chiffon. This mixture filtered out 80-99% of the aerosols, depending on each particle’s size. That percentage is very similar to the efficiency of the N95 masks being used in hospitals all over the world.
Now, if you don’t have an extra nightgown around the house, natural silk or flannel also proved to be very effective combinations when paired with cotton.
As far as why a combination of cotton and chiffon is a cut above the rest, the study’s authors say that cotton, a tightly woven fabric, acts as a mechanical particle barrier. Meanwhile, fabrics like chiffon or silk have a static charge, which provides an added layer of electrostatic protection.
It should go without saying, though, that any mask must properly fit one’s face to be as effective as possible. Just a 1% gap reduced the effectiveness of tested fabrics by 50% or more! Essentially, this means that just a slightly loose mask won’t be nearly as effective. They aren’t always comfortable, but a correctly worn face mask can make all the difference when it comes to stopping the spread of COVID-19.
The full study can be found here, published in ACS Nano.