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Bundles of polyester fibers in a crisscross pattern

Mask fabric top-down view of polyester bundles

Credit: E.P. Vicenzi/Smithsonian's Museum Conservation Institute and NIST
Cross section of woven bundles of cotton flannel fibers

Mask fabrics cross section of a cotton flannel

Credit: E.P. Vicenzi/Smithsonian's Museum Conservation Institute and NIST