Fabric masks prove effective at virus filtration

Testing of commonly available fabric masks has found they significantly reduce the number of aerosolised viruses a wearer could be exposed to, with even the poorest-performing mask filtering at least 50% of viruses.

Conducted by Flinders University researchers, the mask testing was carried out in a special apparatus developed for COVID-19 studies. Viral filtration (VFE) was calculated for two sizes of aerosols: 6 μm, which is the size of aerosols produced by coughing, and 2.6 μm, which are small enough to be inhaled into the lower respiratory system. The fabric face masks tested were purchased from five Etsy retailers based in Australia, chosen at random, and the results were published in the journal Pathogens.

The best-performing fabric masks filtered 97–99% of the virus numbers at both VFE measures, with one mask performing at 98.6% (VFE 6 μm) and 99.1% (VFE 2.6 μm) when made according to the Victorian Department of Health and Human Services guidelines with two layers of re-usable shopping bag fabric and one layer of cotton.

Another mask made from two layers of cotton had a VFE 6 μm of 55% and a VFE 2.6 μm of 93%. However, the effectiveness of this mask increased to become one of the best performers by simply inserting a section of vacuum cleaner bag (VFE 6 μm of 99.5%, VFE 2.6 μm of 98.8%) or a dried baby wipe (VFE 6 μm of 98.5%, VFE 2.6 μm of 97.6%).

While a 50% reduction might not seem particularly effective, US modelling studies have shown that if 80% of the population was wearing a 50% effective mask in areas of high transmission like New York, the number of COVID-19 deaths could fall between 17% and 45%. This predicted reduction in deaths is significantly increased by wearing masks in areas with lower transmission rates, the Flinders researchers said.

“This study gives useful guidance for people who are required to wear face masks in public during the COVID-19 pandemic,” said study co-author Dr Harriet Whiley.

“The information will also inform best practice for fabric face mask design to protect against respiratory diseases and reduce community-based transmission of SARS-CoV-2 (the virus that causes COVID-19).”

Co-author Associate Professor Kirstin Ross added that further research is needed to test face mask design and fitting, noting, “Fit is very important to reduce the risk of viruses entering through gaps between your face and the mask. There also should be an education campaign to inform people about how to wear fabric masks.

“It’s important to wear the mask correctly. Do not touch your mask except to take it off, and wash your mask after use in water that is hotter than 60°C with soap or laundry detergent.”

Image caption: Dr Harriet Whiley demonstrates mask testing. Image credit: Flinders University.

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