  This study explores nonwoven and woven fabrics to improve upon the
performance of the widespread all-cotton mask, and examines the effect of
layering, machine washing and drying on their filtration and breathability for
submicron and supermicron particles. Individual materials were evaluated for
their quality factor, Q, which combines filtration efficiency and
breathability. Filtration was tested against particles 0.5 to 5 micron
aerodynamic diameter. Nonwoven polyester and nonwoven polypropylene (craft
fabrics, medical masks, and medical wraps) showed higher quality factors than
woven materials (flannel cotton, Kona cotton, sateen cotton). Materials with
meltblown nonwoven polypropylene filtered best, especially against submicron
particles. Subsequently, we combined high performing fabrics into multi-layer
sets, evaluating the sets quality factors before and after our washing
protocol, which included machine washing, machine drying, and isopropanol soak.
Sets incorporating meltblown nonwoven polypropylene designed for filtration
(Filti and surgical mask) degraded significantly post-wash in the submicron
range where they excelled prior to washing (Q = 57 and 79 at 1 micron,
respectively, degraded to Q = 10 and 15 post-wash). Washing caused lesser
quality degradation in sets incorporating spunbond non-woven polypropylene or
medical wraps (Q = 12 to 24 pre-wash, Q = 8 to 10 post-wash). Post-wash quality
factors are similar for all multi-layer sets in this study, and higher than
Kona quilting cotton (Q = 6). Washed multi-layer sets filtered 12-42 percent of
0.5 micron, 27-76 percent of 1 micron, 58-96 percent of 2.8 micron, and 72-100
percent of 4.2 micron particles. The measured filtration and pressure drop of
both the homogeneous and heterogeneous multi-layer fabric combinations agreed
with the estimations from the layering model.
