Some face masks may not be effective against Covid

Researchers from the Indian Institute of Science found that certain fabrics and the way the masks were put together played a major role in protecting users

While experts recommend the wearing of homemade face masks when surgical and N95 masks are unavailable to curb the spread of Covid-19, scientists found that not all homemade masks are effective.

Studying how large-sized surrogate cough droplets at different velocities affected masks made out of various locally procured fabrics, researchers from the Indian Institute of Science (IISc) found that certain fabrics and the way the masks were put together played a major role in protecting users.

The researchers looked at how fabric properties, like pore size and porosity, influences droplet penetration through the mask. Using a piezoelectric-based droplet dispenser, the researchers created surrogate cough droplets that impacted a single layer of different fabric samples at different velocities. The fabrics used in the research included single layers of summer stole, handkerchief, cotton towel, and surgical masks.

"Our results show cotton, towel-based fabrics were most effective among the considered fabrics and must be stitched together as multiple layers for making homemade face masks,” said Professor Saptarshi Basu of IISc. “A three or more-layered homemade mask is recommended since it can suppress aerosolisation significantly.”

When the researchers analysed the effect of washing on mask effectiveness, the results showed a negligible influence of washing on mask efficacy for up to 70 wash cycles.

The article, “Efficacy of homemade face masks against human coughs: Insights on penetration, atomization and aerosolization of cough droplets,” was published recently in the journal, Physics of Fluids.