Entire books have been written to cover the basics of this process. A piece of fabric found at the scene can be compared to the suspect's clothing by its weave pattern, twist of the threads, fiber composition, etc. But take it from me, it's a rare case indeed when a CSI stumbles on a piece of fabric, or even a thread. Most of the time you're lucky if you even get fibers. Rayon actually falls between the two categories since it is reconstituted cotton, but is generally considered a natural fiber.
Synthetic fibers start as chemical mixtures and are pulled into long fibers through a sieve.
We'll deal with those in the next article. The most common fiber, period, is cotton. Under a microscope, it looks like flattened tubes, which twist and bend. Any fiber expert will identify it in a heartbeat. Silk also appears tubular, but doesn't twist as much.