A team of researchers claims to have found the best materials for homemade face masks: a combination of either cotton and chiffon or cotton and natural silk, both of which appear to effectively filter droplets and aerosols.

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A new study investigates which materials are best to use for homemade face masks.

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The Centers for Disease Control and Prevention (CDC) have recently updated their guidelines on the use of face masks during the coronavirus disease 19 (COVID-19) pandemic.

The updated guidelines recommend wearing a cloth covering or a mask when it is difficult to maintain physical distancing, such as when shopping.

But research into whether reusable cloth masks can slow the spread of the new coronavirus has resulted in contradictory findings.

For example, some recent studies suggest that reusable masks made of cotton may be ineffective at filtering droplets containing the virus that causes COVID-19: severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

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Could other materials prove more effective? This is the question that researchers — from the University of Chicago and the Argonne National Laboratory, both in Illinois — have aimed to answer in a new study.

Their findings, featured in the journal ACS Nano, suggest that certain fabric combinations may go some way toward halting the spread of the new coronavirus.

In their study, the team experimented with various samples of cotton, chiffon, flannel, silk, spandex, satin, and polyester — on their own and in combination.

They tested the fabric to see if it could filter out tiny aerosol particles. This is because researchers believe that SARS-CoV-2 may disseminate not just through droplets — for instance, from coughs — but also through minute particles that spread when people simply breathe, which are much harder to catch.

The team fanned particles measuring 10 nanometers to 6 micrometers in diameter over the various fabric samples at an airflow rate similar to that of a person’s breath when they are at rest.

The researchers found that a sheet of tightly woven cotton — of 600 threads per inch — plus two sheets of chiffon, made from polyester and spandex, seemed to make the most effective combination, filtering out 80–99% of the particles, depending on their size.

The team even suggests that the performance of this combination is comparable to that of N95 masks, which are used by healthcare professionals.

Other combinations that perform well, according to the researchers, are tightly woven cotton plus natural silk or flannel, and cotton quilt with cotton-polyester batting.

The researchers explain that combinations involving a fabric with a tight weave, such as cotton, and one that can hold a static charge, such as silk, are likely effective because they provide a double barrier: mechanical and electrostatic.

Yet they emphasize that for these masks to be truly effective, they have to fit very snugly.

“The effect of gaps between the contour of the face and the mask, as caused by an improper fit, will affect the efficiency of any face mask,” they write.

“Our findings indicate that leakages around the mask area can degrade efficiencies by [approximately] 50% or more, pointing out the importance of ‘fit’.”

— Abhiteja Konda et al.

Future studies, the researchers point out, should also pay attention to other potentially relevant factors, including the effect of humidity on mask performance and whether reusing and washing homemade masks may reduce their effectiveness.