By Steven Reinberg
TUESDAY, Sept. 22, 2020 (HealthDay News) — Don’t fret about whether that fabric mask you made on your sewing machine protects against the spread of COVID-19 as well as the face masks sold in stores, new research reassures.
Taher Saif, a professor of mechanical science and engineering at the University of Illinois at Urbana-Champaign, examined the effectiveness of common household fabrics in blocking droplets.
“Our goal is to show that many common fabrics exploit the trade-off between breathability and efficiency of blocking droplets — large and small,” Saif said in a university news release.
The team tested breathability and droplet-blocking of 11 common household fabrics. The fabrics ranged from new and used garments, quilted cloths, bedsheets and dishcloths.
“Testing the breathability of these fabrics was the easy part,” Saif said. “We simply measured the rate of airflow through the fabric. Testing the droplet-blocking ability is a bit more complicated.”
Researchers filled the nozzle of an inhaler with distilled water seeded with fluorescent particles that were the size of coronavirus particles.
The inhaler forced the water through the nozzle and made droplets that collected on a dish in front of the inhaler. To test the material they placed it over the collection dish, then repeated the process with different materials.
“We count the number of nanoparticles landing on the dish using a high-resolution confocal microscope. We can then use the ratio of the number collected with and without the fabric to give us a measure of droplet-blocking efficiency,” Saif explained.
The droplets left the inhaler at about 17 meters per second. Droplets from speaking, coughing and sneezing have speeds in the range of 10 to 40 meters per second.
“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 said.
“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,” he said.
The report was published recently in the journal Extreme Mechanics Letters.