Sumit Sankhyan1, Karen N. Heinselman2, Peter N. Ciesielski2, Teresa Barnes2, Michael E. Himmel2, Hannah Teed3, Sameer Patel1, Marina E. Vance This email address is being protected from spambots. You need JavaScript enabled to view it.1,3

1 Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
2 Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA
3 Environmental Engineering Program, University of Colorado Boulder, Boulder, CO 80309, USA

Received: May 24, 2021
Revised: August 3, 2021
Accepted: August 27, 2021

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

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Sankhyan, S., Heinselman, K.N., Ciesielski, P.N., Barnes, T., Himmel, M.E., Teed, H., Patel, S., Vance, M.E. (2021). Filtration Performance of Layering Masks and Face Coverings and the Reusability of Cotton Masks after Repeated Washing and Drying. Aerosol Air Qual. Res. 21, 210117.


  • The filtration behavior of several face coverings was investigated.
  • Doubling surgical masks or layering with a cloth mask can be a better option.
  • Wash/dry study of cotton masks presents strong evidence for their continuous reuse.
  • Cotton cloth masks may offer a biodegradable alternative when reused sustainably.


In this study, filtration efficiency of different respirators, face masks, and a 2-ply cotton handkerchief bandana was compared for particles in the size range of 60 nm–4 µm under a “perfect fit” condition. The filtration efficiency at the most penetrating particle size of 0.3 µm on average ranged from 83–99% for N95 and KN95 respirators, 42–88% for surgical masks, 16–23% for cloth masks, and 9% for bandana. We also investigated the effects of using double surgical masks or layering a cloth mask over various surgical masks in terms of their filtration characteristics. In most of these combinations, the filtration efficiency improved by ~25% for particles 0.3–1 µm in diameter without any substantial change in the filter quality factor when compared to the highest of the individual mask results. To investigate the reusability of cotton cloth masks, 2-layer cotton fabric sample coupons were machine washed and dried for 52 cycles leading to an increase in inhalation resistance (~20 Pa) without affecting size-resolved filtration efficiency. Scanning electron microscopy revealed that washing and drying led to the gradual deconstruction of cotton fibers at the scale of several micrometers to hundreds of nanometers in the form of delamination of the fiber wall and fibrillation of the nanofiber constituents. Results indicate that cloth masks may be layered over surgical masks for additional benefits, and that cloth masks made out of cotton fabric can be washed and reused numerous times without a significant loss in filtration efficiency.

Keywords: COVID-19, Wildfire, Filter quality factor, PPE

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