Assessing effectiveness and comfortability of a two-layer cloth mask with a high-efficiency particulate air (HEPA) insert to mitigate COVID-19 transmission

Abstract

A face mask is essential personal protective equipment to mitigate the spread of COVID-19. While a cloth mask has the least ability to prevent the passage of infectious respiratory droplets through it compared to surgical and N95 masks, the surgical mask does not fit snugly and causes significant air leakage. The synthetic fibers in the latter reduce comfortability and are an allergen for facial eczema. Moreover, the N95 mask causes CO2 inhalation and reduces heat transfer in the nose. Therefore, the objective of the present work is to improve the effectiveness of a two-layer cloth mask by introducing an intermediate, high-efficiency particulate air (HEPA) filter layer. A significant volume of impacted droplets penetrates through a single-layer cloth mask, ejecting secondary droplets from the rear side. However, a two-layer cloth mask prevents this ejection. Despite slowing down the liquid penetration, capillary imbibition through cloth due to its hydrophilicity causes the transport of the liquid into the second layer, resulting in a thin-liquid layer at the mask's rear-side surface and contaminating it. Conversely, the HEPA filter inserted in the cloth mask prevents the imbibition, making the second cloth layer free of contamination. We attribute the impedance to the imbibition by the intermediate HEPA filter layer to its hydrophobic characteristics. We experimentally and analytically assess the role of wettability on capillary imbibition. The breathability measurements of masks show that the HEPA inserted in the cloth mask does not reduce its breathability compared to that of the surgical mask.