Estimating the filtration efficacy of cloth masks

Abstract

The current pandemic has spurred a great deal of debate about the use of cloth masks as effective alternatives to medical masks for the general public. Despite an abundance of experimental studies on the filtration of aerosols by cloth masks, there is currently a lack of analytical understanding to predict mask performance a priori. In this study, we establish a quantitative model for the pressure drop across woven heterogeneous cloth masks and their filtration efficiencies for aerosols with aerodynamic diameters less than 1 μm. To compare the intrinsic filtration capabilities of diverse materials, we introduce a filtration quality factor. Finally, we present a decision map to illustrate the tradeoffs between filtration efficiency and breathability and to provide practical guidance on the purchase of cloth masks. For the most commonly used cotton, polyester, and polypropylene masks, the mechanical filtration capability is fairly independent of the material, but it exhibits a high sensitivity to the porosity and fiber diameter. Additionally, keys to a high-quality cloth mask include a homogeneous structure, micro- or even nanofibrous materials, and a suitable mass per unit area of the textile.