Surgical and N95 Masks Filter Better Than Cloth Ones

A new study strongly corroborates the efficacy of medical-grade masks and highlights the importance of regular washing of homemade cloth masks.

Researchers at the University of California Davis (UCD; USA) conducted an experimental study in 10 volunteers so as to measure outward emissions of micron-scale aerosol particles by healthy humans performing various expiratory activities (including breathing, talking, coughing and moving their jaw (as if chewing gum), while wearing different types of masks. The volunteers sat in front of a funnel in a laminar flow cabinet, which drew air from in front of their faces into a device that measured the size and number of particles exhaled. The tests only measured outward transmission.

Study participants wore either no mask, a medical-grade surgical mask, two types of N95 masks (vented or not), a homemade paper mask, or a homemade one- or two-layer cloth mask made from a cotton T-shirt, according to CDC directions. Without a mask, talking gave off about 10 times more particles than simple breathing, while forced coughing produced a variable amount of particles. Both surgical and N95 masks blocked up to 90% of particles. Homemade cotton masks, in contrast, produced more particles than not wearing a mask, which appeared to be friable cellulosic fibers released from the fabric. The study was published on September 24, 2020, in Nature Scientific Reports.

“The goal of wearing face coverings is to prevent people who are infected with COVID-19, but who are asymptomatic, from transmitting the virus. One of the volunteers in the study was a super-emitter who consistently produced nearly 100 times as many particles as the others when coughing,” said senior author Professor William Ristenpart, PhD, of the department of chemical engineering. “The results confirm that masks and face coverings are effective in reducing the spread of airborne particles, and also the importance of regularly washing cloth masks.”

The N95 designation means that the respirator blocks at least 95% of very small particles, exceeding the capabilities of regular 3-ply surgical face masks.

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