===== Material Recommendations =====

====Best====
  * Soft plastics
    * HDPE
    * LDPE
  * foams.
    * Dence Polystyrene
    * Light weight polystyrene
    * Expanded PVC
  * Cork.

====Noisy====
  * Hard plastics
    * Acrylic
  * Wood
    * Plywood
    * Pine

====Avoid====

  * Solid PVC (Tends to clog bits)
  * Leather (Fibrous. Cuts but clogs bits. Stinks.)