For the last one year or more face masks have become a vital part of human life. Different kinds of masks have been used by people and one of the most common in them is reusable cloth masks.
However, cloth masks have been considered less effective to block coronavirus particles after washing and drying them several times. Now, a study from the University of Colorado Boulder finds that washing and drying reusable cloth masks doesn’t reduce their capacity to filter out viral particles.
The research also confirms previous findings that layering a cotton mask on top of a surgical mask, properly fit on one’s face, provides more protection than cloth alone.
“It’s good news for sustainability. That cotton mask that you have been washing, drying and reusing, it’s probably still fine, don’t throw it away,” said lead author Ms. Marina Vance, assistant professor in the Paul M. Rady Department of Mechanical Engineering
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, who is also on the faculty in the environmental engineering program.
For the research, the team created double-layered squares of cotton, put them through repeated washing and drying (up to 52 times, the equivalent of a weekly wash for a year) and test them between about every 7 cleaning cycles.
The masks were not tested using real people, instead, they were mounted on one end of a steel funnel through which researchers could control a consistent flow of air and airborne particles, the researchers tested the masks using realistic to real-life conditions, with high humidity levels and temperatures to mimics the impact on the mask from our breathing.
While the cotton fibers started falling apart over time, the researchers found that it did not significantly affect the cloth’s filtration efficiency. The only significant change was that inhalation resistance slightly increased, which means that the mask may feel a bit more difficult to breathe through after some wear and tear.
Perfect face mask
The researchers conducted the testing using a “perfect fit” in the lab. “We’re assuming there are no gaps between the mask material and the person’s face,” said Ms. Vance.
The shape of each person’s face varies. So depending on a mask’s shape and how well the person adjusts it, it may or may not fit perfectly. Previous research has shown that a poorly-fit mask can let as many as 50 percent of airborne particles we breathe in and out slip through, as well as the virus.
This is not the first study to find that cloth masks provide less protection than surgical masks or a layered combination of surgical and cloth masks. Measuring how well the mask filtered air being breathed in, this study found that the cotton cloth masks filtered out up to 23 percent of the smallest particle size (0.3 microns) on which the virus can travel. Bandanas filtered even less, at only 9 percent.
In comparison, surgical masks filtered out between 42-88 percent of the tiny particles, and cotton masks on top of surgical masks reached close to 40 percent filtration efficiency. KN95 and N95 masks unsurprisingly performed the best, filtering out 83-99 percent of these particles.
But while this study found that cloth masks alone provide less protection from the virus than a layered approach or disposable masks, such as surgical masks, KN95s and N95s, it remains important information for those who rely on cloth for its comfort, affordability and reusability, said Ms. Vance.
