Don’t throw that cloth mask yet — it still works | Today’s CU Boulder

Reusable cloth masks that have been used for the past year or more may look a little bad when worn. However, a new study from the University of Colorado at Boulder shows that cleaning and drying them does not reduce their ability to filter virus particles.

“That’s good news for sustainability,” said the lead author. Marina Vance, Paul M. Radiy Associate Professor, Department of Mechanical Engineering. “That cotton mask you’re washing, drying, and reusing? Probably not a problem yet. Don’t throw it away.”

Studies published in the journal Aerosol and air quality researchAlso confirms previous studies that layering a cotton mask on top of a surgical mask (which fits the face properly) provides more protection than cloth alone.

Science for sustainability

Since the beginning of the pandemic, an estimated 7,200 tonnes of medical waste has been generated each day, most of which are disposable masks.

“When the pandemic began, we were really worried when we went hiking, going downtown, and seeing all these disposable masks scattered around the environment,” said an environmental engineering program faculty member. Vance said.

So when scientists at the nearby National Renewable Energy Laboratory (NREL) approached her to study the effects of washing and drying on reusable cloth masks, she was keen to work together. ..

Their process was very simple: they created double-layered squares of cotton and repeatedly washed and dried them (up to 52 times, equivalent to weekly washing for a year), approximately every 7 washing cycles. Test

The mask was not tested with real people, but instead was attached to one end of a steel funnel that allowed researchers to control the consistent flow of air and particles in the air. Researchers have tested masks using real-to-real conditions. High humidity levels and temperatures to mimic the effects of our breathing on the mask.

Cotton fibers began to fall apart over time after repeated washing and drying, but researchers found that they did not significantly affect the filtration efficiency of the fabric.

The only notable change was a slight increase in inhalation resistance. This means that the mask can feel a little difficult to breathe after some wear.

Mask fit is important

An important caveat is that we tested it in the lab using “perfect fit”.

“We assume that there is no gap between the mask material and the human face,” Vance said.

The shape of each person’s face is very different. Therefore, it may or may not fit snugly, depending on the shape of the mask and how well the person can adjust it. Previous studies have shown that poor mask compatibility can allow 50% of airborne particles that breathe and exhale to slip through, similar to viruses.

Here you will learn tips and tricks for testing and adjusting masks.

So which mask do you need to wear?

This study is not the first to discover that cloth masks provide less protection than surgical masks or layered combinations of surgical masks and cloth masks.

In this study, cotton cloth masks had the smallest particle size, measuring how well the mask filtered the air inhaled (which protects the person wearing the mask and does not reduce its permeation from the source). It was found that up to 23% of (0.3 micron) was filtered out. The virus can be transmitted. Bandana’s filtering was even less, at just 9%.

By comparison, the surgical mask filtered 42-88% of the small particles, and the cotton mask above the surgical mask reached a filtration efficiency of nearly 40%. The KN95 and N95 masks, of course, performed best, removing 83-99% of these particles.

However, the study found that cloth masks alone were less protective against viruses than layered approaches, surgical masks, and disposable masks such as KN95 and N95, but were comfortable, affordable, and reusable. This is important information for those who rely on cloth for their purposes. Vance said.

“I think the best mask might be the one you actually wear,” Vance said. “And it will fit snugly on your face without being too uncomfortable.”

Other authors of this publication include Sumit Sankhyan, Sameer Patel, and Hannah Teed of the University of Colorado at Boulder. Karen N. Heinselmann, Peter N. Sielsky Teresa Burns, Michael E. Himmel of the National Renewable Energy Laboratory’s Center for Renewable Resources and Realization Science.