The present invention is directed to a method for treating a synthetic, man-made or natural fiber substrate to create a permanently attached protein sheath around each fiber of the substrate. Such a treatment gives a composite substrate that exhibits the most desirable characteristics of the fiber core coupled with the most desirable characteristics of the protein sheath. It is also possible to apply this technology to individual synthetic fibers or yarns, if desired, before weaving, knitting, stitch-bonding or other method of woven or non-woven substrate formation.