During the lockdown, Kreinik retooled several of their machines to make elastic to meet the increased demand. They have added it to their product line. There are two types: flat elastic (in two sizes) and round elastic (in one size).
poly/nylon blend (no latex)
the cone contains 50 yards
3 to 1 stretch, so you don’t have to use as much on a mask
flat elastic comes in 1/8″ and 1/4″ widths
round elastic is about 3/32″ diameter
See the elastic here: http://www.kreinik.com/shops/search.php?mode=search&page=1