I was thinking how to make greaves, Not Cardboard, too stiff, not Posterboard, too Bendable but Plastic Wrap!! Easialy Moldably to make Greaves for a Hoplite, Full wrap-around Greaves for the knights, Beacause after you wrap up the desired Limb, Just cut with a retractable razor ( You might want to wear a pair of jeans for the cutting part)|
Anyway after cutting you simply apply Paper mache to make it rigid! Then add your Decoration.
Hope this helps