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2021 June 25
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Filtration for Wearer Protection
Studies demonstrate that cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns. The relative filtration effectiveness of various masks has varied widely across studies, in large part due to variation in experimental design and particle sizes analyzed. Multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron .14,17-29 Some materials (e.g., polypropylene) may enhance filtering effectiveness by generating triboelectric charge (a form of static electricity) that enhances capture of charged particles18,30 while others (e.g., silk) may help repel moist droplets31 and reduce fabric wetting and thus maintain breathability and comfort. In addition to the number of layers and choice of materials, other techniques can improve wearer protection by improving fit and thereby filtration capacity. Examples include but are not limited to mask fitters, knotting-and-tucking the ear loops of medical procedures masks, using a cloth mask placed over a medical procedure mask, and nylon hosiery sleeves.31-35
Studies demonstrate that cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns. The relative filtration effectiveness of various masks has varied widely across studies, in large part due to variation in experimental design and particle sizes analyzed. Multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron .14,17-29 Some materials (e.g., polypropylene) may enhance filtering effectiveness by generating triboelectric charge (a form of static electricity) that enhances capture of charged particles18,30 while others (e.g., silk) may help repel moist droplets31 and reduce fabric wetting and thus maintain breathability and comfort. In addition to the number of layers and choice of materials, other techniques can improve wearer protection by improving fit and thereby filtration capacity. Examples include but are not limited to mask fitters, knotting-and-tucking the ear loops of medical procedures masks, using a cloth mask placed over a medical procedure mask, and nylon hosiery sleeves.31-35
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A retrospective case-control study from Thailand documented that, among more than 1,000 persons interviewed as part of contact tracing investigations, those who reported having always worn a mask during high-risk exposures experienced a greater than 70% reduced risk of acquiring infection compared with persons who did not wear masks under these circumstances.38