Guidance on the use of face masks during the coronavirus disease 2019 (COVID-19) public health emergency has changed as new information has become available. Although not all major health organizations have recommended face masks for general use, the US Centers for Disease Control and Prevention (CDC) recommends that individuals wear cloth face coverings in community settings, particularly in areas of widespread COVID-19 illness.1,2 This recommendation applies to adults and children aged ≥2 years and is not a substitute for social distancing.

Given this recommendation and others like it from international health organizations, a growing need for masks has led many well-intentioned citizens and organizations to create cloth face masks for themselves and for donation and sale. Some research has shown that cloth masks are only marginally (15%) less effective at blocking particle release than surgical masks.2 Moreover, despite a lack of good-quality evidence in the context of the COVID-19 pandemic, it is clear that cloth masks are more effective than wearing no mask at all.2

The CDC suggests using common, low-cost materials at home to create face coverings,1 but what are the best ones to use? To examine this, one team of researchers from the University of Chicago and other institutions in Illinois investigated the filtration efficiencies of common fabrics, including cotton, silk, and hybrid materials.3 They considered aerosol particles 10 nm to 10 µm in size, which are particularly relevant to viral transmission, and found that a layered mask made of 2 materials was highly effective. In fact, its performance was similar to that of an N95 mask.3


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The hybrid mask contained 1 layer of high-thread-count cotton and 2 layers of natural silk or chiffon (90% polyester and 10% Spandex). “Higher threads per inch cotton with tighter weaves resulted in better filtrations efficiencies,” wrote the researchers. They suggested that the use of multiple materials likely allowed for both mechanical and electrostatic filtering from the cotton and silk or chiffon layers, respectively. “Materials such as silk and chiffon are particularly effective (considering their sheerness) at excluding particles in the nanoscale regime (<~100 nm),” they added. The researchers also found that an experimental mask made from a quilt, which sandwiched a cotton-polyester layer between 2 cotton layers, performed well.3

It is important to note that gaps between the mask edge and facial contours degraded the performance of the masks significantly (by approximately 50% or more). Leakage of exhaled air is an important component of mask effectiveness; the close fit of N95 masks is a major reason why they are so effective when properly worn.3 As such, the researchers emphasized the importance of mask fit and leakage, but concluded that the cloth masks used by large sections of the public during the COVID-19 public health emergency “can potentially provide significant protection against the transmission of particles in the aerosol size range.”3 Overall, masks made from cotton with higher thread counts, natural silk, and chiffon performed well.

References

1. Centers for Disease Control and Prevention. Cloth face coverings: questions and answers. April 4, 2020. Accessed April 24, 2020. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover-faq.html

2. Javid B, Weekes MP, Matheson NJ. Covid-19: should the public wear face masks? BMJ. 2020;369:m1442.

3. Konda A, Prakesh A, Moss GA, Schmoldt M, Grant GD, Guha S. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks [published online April 24, 2020]. ACS Nano. doi:10.1021/acsnano.0c03252