I would highly suggest using EVA foam. I made a Thor suit for my cousin (we're doing the Avengers this year) from 2 types of EVA foam. Have you ever used thin craft Foamies Foam? That's what I used. For the big silver area, I used thick EVA foam pads.
You can get EVA foam pads from places like Harbor Freight. They sell them in a pack, 4 for $10. The Foamies Foam, you can get in many thicknesses. I used 2mm sheets 12 inches by 18 inches. You can get them in a pack of 12 for like, $8.
The reason I suggest you use this instead, is because it is more... eh.. stronger. Ahh, more flexible. That's the word. The 2mm (mili-meter) is VERY flexible and the paint doesnt really mess up. Now, the thicker foam pads will make creases when you when them inward. One side is completely smooth, and the other side has a kind of box-y pattern. It wont mess it up.
You can still use your cardboard as the template. In fact, that's what I used for the template.
Hope this helps!
