Inward and outward effectiveness of cloth masks, a surgical mask, and a face shield

Abstract

We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward 8 protection efficiency on a manikin, and outward protection efficiency on a manikin. At the most 9 penetrating particle size, the vacuum bag, microfiber cloth, and surgical mask had material 10 filtration efficiencies >50%, while the other materials had much lower filtration efficiencies. 11 However, these efficiencies increased rapidly with particle size, and many materials had 12 efficiencies >50% at 2 µm and >75% at 5 µm. The vacuum bag performed best, with efficiencies of 54-96% for all three metrics, depending on particle size. The thin acrylic and face shield performed worst. Inward protection efficiency and outward protection efficiency were similar for many masks; the two efficiencies diverged for stiffer materials and those worn more loosely (e.g., bandana) or more tightly (e.g., wrapped around the head) compared to a standard earloop mask.Discrepancies between material filtration efficiency and inward/outward protection efficiency indicated that the fit of the mask was important. We calculated that the particle size most likely to deposit in the respiratory tract when wearing a mask is ~2 µm. Based on these findings, we recommend a three-layer mask consisting of outer layers of a flexible, tightly woven fabric and an inner layer consisting of a material designed to filter out particles. This combination should produce an overall efficiency of >70% at the most penetrating particle size and >90% for particles 1 µm and larger if the mask fits well. 25.

COVID-19 false dichotomies and a comprehensive review of the evidence regarding public health, COVID-19 symptomatology, SARS-CoV-2 transmission, mask wearing, and reinfection

“…Medical masks have higher and more variable particle penetration rates (~10%-70%) than N95 FFRs (or equivalent), which present low particle penetration rates (<5%) [474][475][476][477][478]. Several filtration studies of cloth face coverings have reported widely variable filtration efficiency and breathing resistance (breathability) estimates depending on the mask design and textile features (i.e., fabric microstructure, permeability, electrostatic properties, number of layers) [467,[479][480][481][482][483][484][485][486][487][488][489][490][491]. Among cloth face coverings, multilayer non-valved masks made of hybrid, closelywoven fabrics show the best filtration efficiency and overall acceptable wearing comfort [55,58,[492][493][494].…”

“…In the face of limited data, face shields or visors have been suggested to provide some advantages over face masks in terms of eye protection, frontward airflow protection, no hand-toface contact, breathability, full-face visibility, reuse, and disinfection [261,[517][518][519][520]. However, variable design (shape, materials) of face shields and upward, downward, and sideways leakage jets from the edges, seams, and joints are major issues [482,500,[521][522][523]. Face shields are therefore considered to provide a level of eye protection only [55,424].…”

A comparison of performance metrics for cloth masks as source control devices for simulated cough and exhalation aerosols

“…The most commonly reported methods have been tests of filtration efficiencies and fit factors (Clapp et al 2021;Guha et al 2021;Konda et al 2020;Wang et al 2020;Zhao et al 2020). Other studies have used manikins in a chamber or room to assess the efficacy of medical masks and cloth masks both as source control devices and as personal protective equipment (Pan et al 2021;Patel et al 2016;Rothamer et al 2021). Experimental data have also been used to develop computational fluid dynamics models of medical and cloth masks performance (Dbouk and Drikakis 2020;Mittal et al 2020).…”

“…The primary purpose of masks (which in this paper includes face masks, neck gaiters, bandanas and other face coverings) is to block the expulsion of infectious droplets and aerosols from the wearer into the environment (called source control) and thereby reduce the exposure of other people to the virus (CDC 2020a). Laboratory studies using manikins and human subjects have shown that cloth face masks can partially block respiratory aerosols produced during coughing, breathing and talking (Asadi et al 2020;Davies et al 2013;Lindsley et al 2021;Pan et al 2021). Wearing medical face masks (i.e., 'surgical masks' as defined by the U.S. Food and Drug Administration (FDA 2004)) reduces the dispersion of potentially infectious aerosols from patients with respiratory infections (Leung et al 2020;Milton et al 2013).…”

“…Wearing medical face masks (i.e., 'surgical masks' as defined by the U.S. Food and Drug Administration (FDA 2004)) reduces the dispersion of potentially infectious aerosols from patients with respiratory infections (Leung et al 2020;Milton et al 2013). Masks may also provide some personal protection to the wearer by reducing their exposure to infectious droplets and aerosols produced by others, although they are not as effective as a respiratory protective device such as a NIOSH-approved N95 filtering facepiece respirator (N95 respirator) (CDC 2020a; Lawrence et al 2006;Oberg and Brosseau 2008;Pan et al 2021). Several community level studies have shown that universal masking helps reduce the spread of COVID-19 (CDC 2020a).…”