Sorry for the delay - had to re-charge the batteries for the camera.
Here's how I did Supes' cape:
(the tape has since been trimmed & shaped to fit so that you can barely see it.)
The wire tie is from any toy package - I shaped it to fit over his shoulders, then glued it to the cape. I had to cut part of the cape around the neck area to look right, and Superglue will darken the material, so I used excess material to "bunch up" around the wire so as to hide the glue job. Then the extra wire is used to secure it to his back - once it's taped (or glued, depending on your preference), you can still shape the wire inside to conform to the figure.
The only reason I use T-shirts rather than bulk material from fabric stores is because it's too hard to find the thin, stretchy Spandex (the best for capes) in bulk. The only material I've found so far was the white I used for Moon Knight's cape - it was sold as "swimsuit liner" material and I got it at JoAnn's Fabrics. Haven't found any more or anything similar since. It doesn't take dye worth a crap, so I've had to look elsewhere for my colored cloth, hence the athletic shirts. This stuff doesn't fray, cuts great, and drapes perfectly over my figs, so that's why I use it rather than regular cloth.
Hope that helps!