I found some heavy fabric that did not fray. I just happened to have some in my fabric bin and it was a perfect shade of blue. This project was as easy as cutting the cape, cutting a whole with two ends, adding a button and button hole as the clasp and then cutting out a mask with the same fabric. I also added a big letter "W" on the back of the cape by cutting out some grey fabric and sewing it on with a regular stitch.
And now I have a Super William flying around most days.