Study: Surgical and Cloth Masks Filter Roughly 10% Efficient at Blocking Aerosols

The commonly worn cloth and surgical masks are roughly 10 percent efficient at blocking exhaled aerosols, a University of Waterloo study found.

The study, examining the effects of masks and ventilation, ultimately found that commonly used cloth and surgical masks do little to filter exhaled aerosols.

“The results show that a standard surgical and three-ply cloth masks, which see current widespread use, filter at apparent efficiencies of only 12.4% and 9.8%, respectively,” the study concluded, noting that KN95 and N95 masks were far more effective at filtering out aerosols.

“Apparent efficiencies of 46.3% and 60.2% are found for KN95 and R95 masks, respectively, which are still notably lower than the verified 95% rated ideal efficiencies,” researchers continued in the data published last month prior to the Centers for Disease Control and Prevention (CDC) reversing course, advising fully vaccinated individuals to wear masks if they are in high-risk areas.

The study’s conclusion continued:

Furthermore, the efficiencies of a loose-fitting KN95 and a KN95 mask equipped with a one-way valve were evaluated, showing that a one-way valve reduces the mask’s apparent efficiency by more than half (down to 20.3%), while a loose-fitting KN95 provides a negligible apparent filtration efficiency (3.4%). The present results provide an important practical contrast to many other previous experimental and numerical investigations, which do not consider the effect of mask fit when locally evaluating mask efficiency or incorporating mask usage in a numerical model. Nevertheless, if worn correctly, high-efficiency masks still offer significantly improved filtration efficiencies (apparent and ideal) over the more commonly used surgical and cloth masks, and hence are the recommended choice in mitigating the transmission risks of COVID-19.

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