OK, thanks. I didn't read that in the article I read so I was confused. Intewesting, because I am making my own masks usually from a knit-type fabric like heavy t-shirt material, so I think it's pretty loose weave. Sometimes I double it, so I guess it's a bit tighter. I'll work on getting it better.

@becsbuddy That is exactly the issue. Bandanas are mad of cheap, loosely woven fabric and IMHO are probably barely better than nothing unless 4 layers thick. Mo other objection to bandanas and similar designs is that they are loose at the bottom, therefor of limited use in containing droplets.
As far as the knitted neck gaiters, the reason knit fabrics tend to be comfortable to wear, in clothing and masks, is the permeability - so unless a filter layer is incorporated in the mask, vapor is readily passing through. My knowledge goes back to fiber study days - the holes created by the knitting process are multi-diemensional, and therefore more permeable than a tightly woven fabric of similar weight. The reason high-quality sheets and quilting cottons are recommended is their high thread count - 400 or more threads per square inch. Doubled or tripled, they are even better.
The other reason gaiters rend to be less useful is that they don't fit firmly near the nose due to the stretch factor, again allowing more vapor to escape.
Sue