Fabric scrunchies are the most common variety.
Many types of fabric can be used for scrunchies. The best types are fabric that has some grip to it, such as cottons and cotton blends. Silkier fabrics do not grip the hair but may make a lovely decorative hair tie for a special occasion. Because of the small amount of fabric needed for each scrunchie, less than a quarter of a yard, sewing them from scrap fabric left over from other projects is viable.
A simple tube sewn around an elastic strip is all that is needed. Knot the elastic strip and sew the tube shut. The elastic strip can be secured to the outer fabric with a line of stitches or can remain free to move about within the tube. The benefit of leaving the elastic to move freely within the tube is that if the elastic breaks, you only need to undo one line of stitching to repair the scrunchie. If the elastic is secured to the fabric tube, you may need to undo several lines of stitching.