The quickest and lightest way to increase strength in your model structures. Use the smallest of the carbon rods to brace the tails of your foam profile planes, or make up you own carbon pushrods from rod or tube. Add a length of carbon rod to the leading edge of your foam model to make it impervious to the dings that are common while landing. Laminate some carbon strip to the sides of a spar to make it radically stronger, but not a lot heavier. Can be glued with CA, epoxy or Uhu Por.