[skipwalker]

This website chose cotton t-shirts as the best combo

https://smartairfilters.com/en/blog/diy-homemade-mask-protec...

https://smartairfilters.com/en/blog/best-materials-make-diy-...

[greedo]

Dish towels and vacuum bags do a better job of filtering, but make breathing quite difficult. A simple cotton t-shirt material is fine. And there's no sign that double layers help; and they make it harder to breath as well.