CMC stands for carboxymethyl cellulose. It's a powder that makes the sugar paste thicker/firmer (the formed parts hold the shape better) and speeds-up the drying time. Other names for CMC are tylose powder and tylo powder.

CMC is NOT the same thing as gum tragacanth. CMC is a synthetic substitute for gum tragacanth. CMC works quicker than gum tragacanth, so you don't have to wait many hours for the paste to get thicker/firmer.
How do you know if you have added the right amount of CMC:
  • You can roll a smooth ball that doesn't lose the shape (see the photo below).
  • The paste is soft enough to model the part (get the shape you want).
  • The modelled part holds the shape well.
  • The part (after leaving it for some time to dry) doesn't sink under the weight of other parts. The more CMC you add, the quicker it will become firmer.