https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/masking-science-sars-cov2.html
Multi-layer cloth masks block release of exhaled respiratory particles into the environment,3-6along with the microorganisms these particles carry.7,8 Cloth masks not only effectively block most large droplets (i.e., 20-30 microns and larger)9 but they can also block the exhalation of fine droplets and particles (also often referred to as aerosols) smaller than 10 microns ;3,5which increase in number with the volume of speech10-12 and specific types of phonation.13Multi-layer cloth masks can both block up to 50-70% of these fine droplets and particles3,14 and limit the forward spread of those that are not captured.5,6,15,16 Upwards of 80% blockage has been achieved in human experiments that have measured blocking of all respiratory droplets,4with cloth masks in some studies performing on par with surgical masks as barriers for source control.3,9,14
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