The worldwide shortage of single-use N95 respirators and surgical masks due to the COVID-19 pandemic has forced many health care personnel to use their existing equipment for as long as possible. In many cases, workers cover respirators with available masks in an attempt to extend their effectiveness against the virus. Due to low mask supplies, many people instead are using face coverings improvised from common fabrics. Our goal was to determine what fabrics would be most effective in both practices. Under laboratory conditions, we examined the hydrophobicity of fabrics (cotton, polyester, silk), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19. We also examined the breathability of these fabrics and their ability to maintain hydrophobicity despite undergoing repeated cleaning. Laboratory-based tests were conducted when fabrics were fashioned as an overlaying barrier for respirators and when constructed as face coverings. When used as material in these two situations, silk was more effective at impeding the penetration and absorption of droplets due to its greater hydrophobicity relative to other tested fabrics. We found that silk face coverings repelled droplets in spray tests as well as disposable single-use surgical masks, and silk face coverings have the added advantage over masks such that they can be sterilized for immediate reuse. We show that silk is a hydrophobic barrier to droplets, can be more breathable than other fabrics that trap humidity, and are re-useable via cleaning. We suggest that silk can serve as an effective material for making hydrophobic barriers that protect respirators, and silk can now be tested under clinical conditions to verify its efficacy for this function. Although respirators are still the most appropriate form of protection, silk face coverings possess properties that make them capable of repelling droplets.

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Background The worldwide shortage of single-use N95 respirators and surgical masks due to the COVID-19 pandemic has forced many health care personnel to prolong the use of their existing equipment as much as possible. In many cases, workers cover respirators with available masks in an attempt to extend their effectiveness against the virus. Due to low mask supplies, many people instead are using face coverings improvised from common fabrics. Our goal was to determine what fabrics would be most effective in both practices. Methods and findings We examined the hydrophobicity of fabrics (silk, cotton, polyester), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19. We also examined the breathability of these fabrics and their ability to maintain hydrophobicity despite undergoing repeated cleaning. Tests were done when fabrics were fashioned as an overlaying barrier and also when constructed as do-it-yourself face coverings. As a protective barrier and face covering, silk is more effective at impeding the penetration and absorption of droplets due to its greater hydrophobicity relative to other tested fabrics. Silk face coverings repelled droplets as well as masks, but unlike masks they are hydrophobic and can be readily sterilized for immediate reuse. Conclusions Silk is an effective hydrophobic barrier to droplets, more breathable than other fabrics that trap humidity, and are readily re-useable via cleaning. Therefore, silk can serve as an effective material for protecting respirators under clinical conditions and as a material for face coverings.