This is useful stuff for making ties for masks in place of elastic. I’m not sure it’s comfortable for behind the ears but it’s great for ties.
The sort of shirt without side seams is preferable. Cut off the bottom from just under the armpits.
Using scissors or a rotary cutter, cut the lines started at one side and stopping about 2" from the other side as shown. It is important NOT to cut all the way through.
This is the magical part: starting at one end, firmly grasp the yarn in both hands and stretch it, pulling the yarn through your hands from one end to the other. This causes the edges to curl up into a rounded yarn shape. I got yards and yards of it from just one shirt!
I’ve been working my way through my huge stash of tee shirt yarn for making ties for masks! So much softer and more comfortable to wear than bias tape.