Filtration efficiencies (FE), pressure drops (ΔP) and construction parameters were measured for 27 cloth materials (12 cotton, 8 full synthetic, 3 synthetic blends, 4 synthetic/cotton blends) used in cloth masks intended for protection from the SARS CoV-2 virus (≈ 110 nm). Seven polypropylene-based fiber filter materials were also measured, including from surgical masks and N95 respirators. Additional measurements were performed on both multi-layered and mixed- material samples of natural, synthetic, or natural-synthetic blends to mimic cloth mask construction methods. Materials were micro-imaged and tested against size selected NaCl aerosol with aerodynamic diameters between ≈ 90 nm and ≈ 1.12 µm. Woven cotton samples had higher FE compared to synthetic samples. The mixed material samples did not exhibit a significant difference in the measured FE when compared to the sum of the individual FE for the components, as has been previously posited. The FE and ΔP increased monotonically with the number of cloth layers, suggesting that multilayered cloth masks may offer increased protection from nanometer- sized aerosol with a maximum FE dictated by breathability (i.e. ΔP).
COVID-19, face mask, filter, particle counting, fabric properties