Cut the fabric for the cape into a large rectangle. Save the leftover fabric for the mask and cuff. Here is a list of cape sizes for a various ages: 12 months to 2T = 36” x 16”; 3T to 5T = 36” x 20”; 6 to 8 years = 36” x 24”; 8 to 10 years = 36” x 27”.
For the cape, use liquid metal fabric. Typically it can be found in the costume-fabric section at most large-name fabric stores. Liquid metal fabric doesn’t fray, so no need to worry about hemming or other more time-consuming sewing techniques. Other fabrics that are easy to work with that you might consider for the cape include flannel, fleece, knit and some other costume fabrics. These may not have the same lightweight airy feel to them, but will work.