Mid 2021 update: High thread count cotton and/or multi-layer polyester satin isn't a good choice for high filtration masks. They're not breathable enough at mid filtration performance. And additional layering to get to hight filtration still only decreases breathability further. With that they get hot and uncomfortable as well as giving your chest muscles a good workout.
750 thread count cotton is very high filtration (so says Konda et al in
https://pubs.acs.org/doi/pdf/10.1021/acsnano.0c03252). Nobody talks about it, but it is not very breathable. It pull onto your nostrils and lips as you breathe in. That's no good as the surface area gets smaller when that happens, and there's you need a large surface area to breath in through for such a fabric. That's NOT a lower oxygen scenario, it is a PRESSURE DROP scenario. You chest muscles have to be stronger to pull air through it (or the surface area needs large enough). 99.9% of the cloth masks out there won't be a problem to breath through - only the multi-layer ones or higher thread count ones will.
Thus, you put in something to force a 3D shape. For many N95 masks the material is thick enough to retain a cupped shape as you breathe in.
In this case of THIS mask, a cut-up plastic placemat from the supermarket is clipped in. This placemat is a mesh - water would pour through it, and air has no problem passing through it. I've sewn in some acetate-satin bias tape for this "RETAINER" to clip into. It is removable for washing.
Pics:
The satin-acetate bias tape as sewn into the inside of the mask:
All together this mask works well. You would remove the plastic retainer before you wash the mask. You would wash it each night - hand wash with warm soapy water is best. Drying is a challenge - if you're in a humid climate it won't dry on washing line outside.
There's no filter pocket. That is not needed the 750-tc cotton and satin are very high filtration (per Konda et al). The nose wire is sewn inside the mask, fairly early on. You could wear this all day (but you would wash it daily).
Alternate (older) retainers shapes/materials:
The lighter grey one is IKEA SNOBBIG (I only had two narrow strips so I sewed them together - imperfect of course)
And yet more retainers since this original post:
Polypropeline placemat snipped by hand, then hole-punched, then craft-knifed:
Ones Zack has made on a 3D printer:
Here's me in in OmniGraffle thinking up something (no made yet):
And with nostril cutouts:
A different take that Lesley is working on (laser cutter) that clips together into 3D shape without that being spring loaded:
And another design I've done in OmniGraffle but not yet had laser cut:
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