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Researchers at Duke University have developed a simple, low-cost method to assess the efficacy of different face masks at reducing the transmission of respiratory droplets during normal speech. Respiratory droplets are believed to be the primary way that people spread SARS-CoV-2 to one another. The described experimental setup consists of a green laser, a cylindrical lens, a cell phone camera, and an enclosure with slits for the light to shine through, as well as hole for the speaker’s face.

The team found that the best performing mask was, perhaps unsurprisingly, a fitted N95 respirator. The 2-layer polypropylene apron mask and cotton-polypropylene-cotton masks also did well. Among the worst performers were the double-layered bandana and gaiter type neck fleece. The research article, titled “Low-cost measurement of facemask efficacy for filtering expelled droplets during speech,” was published in Science Advances and is available for free.