Two coordinating knit fabrics or Tshirts
Elastic (1/4 inch wide)
If you're using Tshirts to make this, cut a 6 inch wide strip from the bottom of Tshirt, including its hem. The benefit of using Tshirts is that you could use the hem as an elastic casing. Just unpick a few stitches from both ends of the strip.
Sew a seam at the 6 inch sides ( right sides together)
Set your machine tension on high, stitch length maximum and sew a seam on one of the raw sides of the strip. This will gather the strip.
Sew a seam on the shorter sides ( right sides together).
Cut another 5 inches strip and repeat the above steps.