Largely inspired by this excellent Say Yes to Hoboken Turban Twisted Scarf tutorial and a Forever 21 elastic headband, I made a twisted headband with an elastic back. I used a fat quarter from Joann's (with leftovers remaining) and 1/2" elastic.
I folded the fabric in half and free-handed a template to cut out four identical oval shapes.
Next, I sewed the pieces right sides together with a 1/4" seam allowance, leaving a gap on the side to turn them inside out.
Crossing the two pieces and pinning the ends together. I sewed a small line across each end to connect the folded halves together.
For the elastic across the back I made a small tube about twice as long as the elastic piece which ended up being about 5 inches (based on rough measurements after seeing how long the rest of the headband was on my head).
The rectangle measured about 2"by 10".
For the elastic, I used a safety pin to guide the elastic through first. I sewed one end down to the main part of the headband in a triangular shape and did the same to the other side securing the elastic as well.