Surgical masks stop more than 90% of the droplets emitted by speech, according to a comparative study of 14 types of masks which concludes that bandanas and fleece neck warmers are the least effective. For this experiment published by Science Advances on August 7, researchers from the American University of Duke made several masked participants talk in a dark room towards a laser beam, the scene being filmed (people repeated: " Stay healthy, people " , " Take care of yourself "). The number of postilions and droplets crossing the ray was analyzed by computer.
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Unsurprisingly, masks reserved for hospital staff N95 (the US standard, equivalent to FFP2 in Europe) are the most effective, reducing droplet transmission by more than 99.9%, compared to a person speaking without a mask. Three-layer medical masks followed, which reduced it by over 90%, and just behind polypropylene and cotton / polypropylene masks. For homemade cotton masks, the reduction ranged from 70% to 90%, depending on the number of layers and pleating. Bandanas reduced droplets by 50%.
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The worst of the 14 masks tested was a fleece neck warmer, the type runners use: this fabric actually increased the number of droplets expelled, possibly because the material split the large droplets into smaller ones. N95 professional medical masks equipped with a round valve were finally much worse than the N95 without valve and comparable to cotton masks, because the valve precisely helps to evacuate the exhaled air; these masks are sold as " breathable ", but authorities and experts advise against them because, if they protect the wearer, they more easily spread the contaminated air exhaled by a person.
