Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

Abstract

The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10 μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, respectively, the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton−silk, cotton−chiffon, cotton−flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.

Utility of Cloth Masks in Preventing Respiratory Infections: A Systematic Review

“…In both studies the filtration efficacy dropped significantly in the presence of leakage. 12 also found that in the presence of leakage, the efficacy of all masks decreased by about 50% or more.…”

“…In some cases, the efficacy of cloth masks has been reported to be higher than 90%. In the study by Konda et al 12 double layered cotton with 600 threads per inch showed a filtration efficacy of 99.5 ± 0.1% in the >300 nm particle range compared to 99.9 ± 0.1% efficacy of N95 masks in the same range. Although less than the N95 masks in most cases such high efficiency of some types of cloth masks raises the hope of them being useful against droplet infections.…”

“…The cloth masks are also rarely fit tested which causes significant decrease in efficiency due to leakage, which may be up to 50% or even more. 12 In the healthcare setting, cloth masks were found to be inadequate 5 in preventing influenza like illness compared to the surgical masks (relative risk 13.25, 95% confidence interval 1.74 to 100.97). However, the conclusion must be drawn carefully as there was no arm without mask.…”

“…5 The second paper used the data from the first trial to assess the compliance of the healthcare workers to cloth masks and surgical masks. 6 Seven of the non-clinical studies measured filtration efficacy of cloth masks [7][8][9][10][11][12][13] and the remaining study analyzed the microscopic properties of cloth masks. 14 Risk of bias assessment of the randomized controlled trials is provided in table 1.…”

Quick laboratory methodology for determining the effectiveness of face mask respirators in the wake of COVID-19 pandemic

“…As infected individuals release considerable numbers of submicron particles in the exhaled breath 15,16 , detailed measurements in this size range have also been reported 17,18 . These mostly include electrical mobility measurements for interpretation and methodology development [19][20][21] .…”