Hold a piece of cardboard flush against the chest and midsection of the person for whom you are making the costume. Have a helper hold the cardboard if the costume is for you. Trace an outline of the chest and midsection. Repeat this process with a second piece of cardboard for the person's back. Cut the pieces along the outlines.
Wrap both pieces of cardboard in foil. The foil gives the cardboard a metallic and reflective look. Measure and break different pieces of plastic foam. Wrap plastic foam pieces in foil as well. Glue the pieces to the first cardboard piece. Get creative on how to use and place the plastic foam. For example, break off or cut six 1-by-3-inch pieces. Align and glue them onto the front piece of cardboard to resemble strong abdominal muscles. In lieu of foil, use spray paint, markers, glitter and/or crayons to add a vibrant look to the armor.
Punch a small hole in the upper corner of each piece of cardboard. Thread string or ribbon through the holes: one piece of string connecting the left side of each piece of cardboard and one piece of string connecting the right side. Allow 5 or 6 inches of slack. Pull your head up between both pieces of string and rest each piece of string comfortably on both your left and right shoulder. You are now wearing your futuristic armor. Have fun.