Its a very nice cloth effect
I can sculpt .. But I've never tried to make capes for a mold.... but I'd be interested to see how that cape looks from the other side.
Or if you were wanting to make a one off cloth effect using sculpey try running it through a pasta machine at the thinnest setting.
Very fine sculpey tends to fold like cloth. You just have to put the folds and creases in where you want.