SEM characterizations of three layers in Bacou Willson 801 N95 FFR.

( a-b ) SEM images of cross section. ( c-e ) SEM images of top down view of pristine Bacou Willson 801 N95 FFR. ( f-h ) SEM images of top down view of the of Bacou Willson 801 N95 after heat treatment at 100°C for 4 cycles. ( i-k ) SEM images of top down view of the of Bacou Willson 801 N95 after steam treatment. The morphologies of dry air heat treatment and steam (autoclave) treatment do not show obvious difference from SEM images, which indicates the morphologies are not changed under the dry air heat treatment and steam treatment methods used. (TIFF)