Rin,
Rayon basically starts from wood pulp. It is treated (with harsh acids and bases) and processed (i.e. spun, etc) during the manufacturing process. The basic procedure is a) Break down and extract the cellulose from the wood, b) Re-spin the cellulose into long, fine fibers. So it's basically a purification stage, followed by a "re-assembly" stage. Rayon is a manufactured material, although the raw material is basically wood. I wouldn't say the fibers are "treated" with chemicals, rather they are "created" with chemicals.
If you'd like the details of the whole process typically used:
Rayon - Wikipedia, the free encyclopedia
Although the process sounds pretty nasty, it is a very effective process for getting
pure cellulose fibers as the end result. The chemicals used (Lye, carbon disulfide and Sulphuric Acid) aren't things I'd like to keep around the home, but they are simple and powerful chemicals that do the job of purification very well. Someone commented earlier that "This stuff is so white, it must have some chemical treatment done to it" but the fact is, it's so white because it is basically very pure material. Things like the glaze used on your coffee cup have much more potential for harmful contaminants.
It is up to you whether or not to trust this as a wicking material, but I hope you can see the difference between the process and the product!
