I made armor waist piece out of EVA foam. I did it by gluing together multiple pieces to make it look like different plates, it also helped me to curve the armor for a more hourglass shape.
I also put a zipper in the back and reinforced the inside cracks with hot glue.
Here's the "underwear" piece =)
And I also remade the top chest piece. I found the craft foam easily dented and didn't retain its shape I wanted. It's good for detailing but I decided I don't like it for big armor pieces.
Here it is all together:
Going to start painting everything very soon...