DIY - Make a Duct-Tape Dress Form by David Coffin, THREADS Mag. Use Duct-tape as both the body-casting material & the final form. 2 different methods shown in articles. "Duct-Tape Dress Form" article & "more difficult "Closer-Fit Duct-Tape Dress Form.
While this armor look-a-like would be extremely non-functional, the tutorial for this is pretty neat. I could see using this method on small details of a costume. Although, the perfectionist in me would prefer the armor to be real.