(just sent this in a PM and thought the info could be helpful to someone else)
Craft foam (aka fun foam or foammies) is like one of GODS many gifts to this world..no lie.
You can buy it in most craftstores like Joanns, michael's and even in some wal-marts. They come in different gauges. The standard is 0.2mm (comes in sheets and rolls. It is thin and tears easy if not re-enforced). 0.3mm comes in decent sized sheets (flexible and not as easy to tear) and 0.6mm comes in small 8x10 sheets (very thick, not very flexible and difficult to tear).
I used the 0.2mm since it was the cheapest & is sold in rolls. Now that I have a little bit more knowlege about craftfoam (thanks to Jania Solo's craftfoam panel at Phoenix Comic-con), i'd recommend using the 0.3mm to give you more durability and stability.
For the detailing I cheated and used 3-D Fabric paint instead of cutting each piece out of craft foam. Then after the fabric paint dried, I painted the whole piece of armor with black acrylic paint.
A Few Helpful Links :
*I did a slight re-color on Fran, to break up all the black
Saboten-Con 2009: Best Novice
Appears in Cosmode issue #29