In an effort to provide a most efficient and safe product, all PB non-medical masks will now include ear loops made in a softer stretchier elastic equipped with plastic stoppers for an adjustable more secure and comfortable fit.
from New York Times article April 10, 2020 A User’s Guide to Face Masks
"Cotton quilting fabric: This is the high-thread-count cotton fabric preferred by quilters for its durability. In studies at Wake Forest Baptist Health, masks made with quilting fabric rivaled the filtration efficiency of surgical masks."
from Explore Health
The study found that so-called “quilting cotton” was generally much better than the sort of printed fabric available in discount fabric stores. “It tends to have the characteristics we found most effective: thicker, heavier yarn, higher thread count, tighter weave,”