CHAMPAIGN, Ill. — Health officials widely agree that a face mask is fastest and easiest way to help stop the spread of coronavirus. For people making their own coverings at home, the biggest question usually is what fabric to use. While some materials may be more comfortable than others, a new study finds most homemade masks are doing the job just fine. Researchers say, even when sneezing, a homemade mask can block infectious droplets with as few as one layer.
A team from the University of Illinois says aerosol particles (tiny droplets) are typically five micrometers in size or smaller. Aerosols are one of the key ways scientists believe COVID-19 is transmitted from one person to another. Larger droplets however, around one millimeter in diameter, can also be expelled as people talk, cough, and sneeze.
While regular face masks can usually stop these potentially infectious particles, the research team is studying to see how household fabrics do as well. The fear is, with enough momentum, large particles could squeeze through certain materials, break into smaller aerosols, and become airborne.
Mechanical engineer Taher Saif and his team examined the breathability and droplet-blocking ability of 11 household fabrics. These included new and used clothing, quilted cloths, bedsheets, and dishcloths.
“Testing the breathability of these fabrics was the easy part,” Saif says in a university release. “We simply measured the rate of airflow through the fabric. Testing the droplet-blocking ability is a bit more complicated.”
Homemade face masks ‘considerably effective’
To test a fabric’s droplet blocking power, researchers filled an inhaler with water mixed with 100-nanometer fluorescent particles. Study authors say the size of these particles is the key because that’s also the size of novel coronavirus particles.
When the inhaler was puffed, water was projected from the nozzle at high speed just like a cough or sneeze. Placing each fabric in front of the inhaler, the study examined how well each did at stopping the COVID-sized particles.
“We found that all of the fabrics tested are considerably effective at blocking the 100 nanometer particles carried by high-velocity droplets similar to those that may be released by speaking, coughing and sneezing, even as a single layer,” Saif reports.
“With two or three layers, even the more permeable fabrics, such as T-shirt cloth, achieve droplet-blocking efficiency that is similar to that of a medical mask, while still maintaining comparable or better breathability.”
Balancing effectiveness with comfort
One of the tricky things about making a homemade mask, researchers find, is balancing form with function. Saif says a person generally wants to feel comfortable with the face covering they have. While a mask made with thicker material count may stop more particles, it can be useless if not worn properly.
“A mask made out of a low-breathability fabric is not only uncomfortable, but can also result in leakage as the exhaled air is forced out around contours of a face, defeating the purpose of the mask and providing a false sense of protection,” the mechanical science and engineering professor adds. “Our goal is to show that many common fabrics exploit the trade-off between breathability and efficiency of blocking droplets – large and small.”
The study appears in the journal Extreme Mechanics Letters.