Regenerated cellulose. The Code of Federal Regulations defines rayon as a manufactured fiber composed of regenerated cellulose, as well as manufactured fibers composed of regenerated cellulose in which substituents have replaced not more than 15 percent of the hydrogens of the hydroxyl groups. Now produced almost exclusively by the viscose process. Review: J. Lundberg, A. Turbak in Kirk-Othmer Encyclopedia of Chemical Technology Vol. 19 (Wiley-Interscience, New York, 3rd ed., 1982) pp 855-880.