"Wearing cloth masks reduced the exposure to some extent," but "the most commonly used cloth mask products perform poorly when compared to alternative options available on the market," said the study by scientists at University of Massachusetts Amherst. In a series of experiments with an experimental mannequin in Nepal, the researchers tested four masks -- one pleated surgical type, two cloth and one cone-shaped cloth with exhalation flaps. They tested for several variables and effectiveness in filtering out five different synthetic aerosol particle sizes plus three particle sizes of diluted whole diesel exhaust, which simulated real-world conditions.
Among the cloth masks, the one with exhaust valves performed fairly well, removing 80-90 percent of synthetic particles and about 57 per cent of diesel exhaust. Plain cloth masks were "only marginally beneficial" they said, in protecting people from particles smaller than 2.5 micrometers, often considered more harmful than larger particles because they can penetrate the lungs more deeply.
"Unfortunately, the least effective two mask types are also inexpensive, reusable and are widely used in developing countries, implying they are a popular consumer choice where pollution mitigation is warranted," the authors noted.