All polymer clay requires conditioning.
This is extremely important because the plasticizers in the clay move when the clay sits. Prior to using the clay, it is important to make sure that these plasticizers are mixed back into the clay uniformly. A good rule of thumb that you have sufficiently conditioned your clay is that, when you run the clay through a pasta machine, the edges of the clay remain smooth and don't break apart. By the time the colors are thoroughly mixed together, your clay should be sufficiently conditioned. Original Fimo and Cernit require more conditioning than most of the other clays because it is not as soft as the other clays out of the package.