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Originally Posted by glatt
The fit and breathability of the mask are just as important as the filtration. Possibly more important.
If the fabric weave of the mask is too tight, with a really high thread count, or too many layers, it just acts as a diverter to funnel your breath out the sides and around your nose. Nothing gets filtered.
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From the first article I linked:
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... The single layer covering was made from a folded piece of cotton T shirt and hair ties; the double layer covering was made using the sew method, as set out by CDC: ...
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Seems like they were looking at expendable clothing as a common denominator.
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... This is just one case, added to which several other factors contribute to the effectiveness of cloth face masks, note the researchers. These include the type of material used, design and fit, as well as the frequency of washing. ...
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You left out frequency of washing.