Use a t-shirt...
I honestly thought this was like the elastic cord I previously used. The cord is definitely like the one in the one photo with the n95 mask. I will save you a bunch of money. When I started making masks, I had a little elastic, used it up, and then could not find it anywhere. After two attempts of buying on ebay since all of the amazon ones said they could not deliver until June/Julyish, and not receiving, I came back to look on amazon. While waiting for this to arrive, I tried using a stained white shit I had and was ready to toss. I cut in strips and then stretched the string (make sure the shirt is stretchy cotton...if it isn't,you can still do it but you will have to make it like bias tape and make a tie mask). It worked fabulously. I was actually thinking about canceling this shipment except it already shipped. I got this and that is EXACTLY what I had been using with the cut up shirts. The only benefit is that it is pre-cut and all even, other than that, it is identical. It is a softer cotton, and stretchy. This is NOT regular elastic that would be on a mask, this is literally strips of stretchy cotton. It works, but it may not be what some people expect, so just giving a heads up. Gave it 3 stars because the title is misleading enough where I am sure people will assume that this is regular 1/4" elastic cord, which it isn't.
Rating: 3 stars