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Reusable face masks retain their ability to filter coronavirus particles after a year of washing and drying them, a US study has found.
“It’s good news for sustainability,” said lead author Marina Vance, assistant professor in the Paul M. Rady Department of Mechanical Engineering at the University of Colorado Boulder.
“That cotton mask that you have been washing, drying and reusing? It's probably still fine - don't throw it away.”
Since the start of the pandemic, an estimated 7,200 tons of medical waste has been generated every day - much of which is disposable masks.
“We were really bothered during the beginning of the pandemic, when going out on a hike or going downtown, and seeing all these disposable masks littering the environment,” said Ms Vance.
In an attempt to reduce this waste and deter people from disposing of their cotton masks, she joined forces with scientists at the nearby National Renewable Energy Laboratory (NREL).
The process they set up was quite simple: create double-layered squares of cotton, put them through about 52 wash and dry cycles - the equivalent of a weekly wash for a year - and test them between about every seven washes.
Imitating real-life mask-wearing conditions
To test their efficacy, the washed masks were mounted on one end of a steel funnel through which researchers could control a consistent flow of air and airborne particles. The testing environment was hot and humid to mimic the impact on masks from our breath.
Although the cotton fibres started falling apart over time after repeat washing and drying, researchers found it didn't significantly affect the cloth’s filtration efficiency.
The only noticeable change was that inhalation resistance slightly increased, meaning the mask may feel a bit more difficult to breathe in through after some wear and tear.
A key caveat is that researchers carried out the tests on perfectly fitting masks.
“We're assuming there are no gaps between the mask material and the person's face,” said Ms Vance.
Previous research has shown that a poorly fitting mask can let almost 50 per cent of airborne particles we breathe in and out slip through - as well as the coronavirus.
Ms Vance acknowledged that cloth masks don't perform as well as surgical masks like KN95s and N95s, but says the findings remain important for those who rely on cloth for comfort, affordability and reusability.
“I think the best mask might be the one that you're actually going to wear and that is going to fit snugly against your face without being too uncomfortable," she said.