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Table 2 Average filtration efficiency and standard deviation across mask type. KN95 masks had the largest variability in filtration performance out of all mask types tested, with a filtration efficiency standard deviation of 33.63% as compared to 0.51% and 1.23% for FFP2s and N95s respectively

From: Assessing the filtration efficiency and regulatory status of N95s and nontraditional filtering face-piece respirators available during the COVID-19 pandemic

Mask Type Mean Filtration Efficiency (%) Filtration Efficiency Standard Deviation (%)
FFP2 (n = 4) 99.3 0.51
KN95 (n = 33) 81.1 33.63
N95 (n = 15) 98.0 1.23