We recently visited a silicone compression molding factory with our friends at Dangerous Prototypes. This is the same technology used for making our silicone keypads for the T400 temperature datalogger.
I put together a short video showing the overall process. The process begins by mixing a base material with colorant using a roller machine similar to a pasta maker. Then chunks of the material are placed in a mold, which then enters a press. The silicone is compressed and takes the shape of the mold. The mold is then heated and the material cures in a few minutes.
On this particular day the factory was making some adult toys, but the process is the same for keypads and other parts.