Structural comparison of commercially available face masks using scanning electron microscopy

The fabric structures of re-usable (cotton, polyurethane, polyester 95% with polyurethane 5%, polyester 95% with spandex 5%) face masks compared to disposable non-woven masks were observed under scanning electron microscopy. We found re-usable face masks in general have homogeneous pore sizes of approximately 0.1 - 0.5 mm. In comparison, non-woven masks have two fiber layers separated by one densely non-woven labyrinthine layer with disordered three dimensional microfibers. We found most (7 out of 8) non-woven masks shared this similar dense second layer composition. Our observation for masks under the electron microscopy provides structural evidence underlying infection-preventing superiority of non-woven over re-usable (cotton, polyurethane, polyester 95% with polyurethane 5%, polyester 95% with spandex 5%) face masks. Furthermore, we found that non-woven masks do not always have the disordered dense middle layer, which suggests that some products of non-woven masks may not provide equal protection for infection.