Method of treating synthetic fibers or synthetic fiber fabrics

A method of treating fiber made of synthetic polymer or a fabric comprised of said fiber, which comprises the steps of:

• applying to said fiber a first aqueous solution or an aqueous dispersion containing a heat-stable polymerization initiator and heat treating said fiber in a first heat treating step until from 0.01 to 5 percent by weight of said polymerization initiator, based on the weight of said fiber, penetrates into and is retained in the interior of said fiber;
• then washing said fiber with water to remove polymerization initiator remaining on the surface of said fiber;
• then applying to said fiber a second aqueous solution of at least one water-soluble polymerizable monomer capable of being polymerized by contact with said polymerization initiator to form a hydrophilic polymer for imparting a water absorption property and an antistatic property to said fiber, said second aqueous solution having a pH of not higher than 6, and heat treating said fiber in a second heat treating step at a temperature effective to polymerize said monomer to form said hydrophilic polymer wherein said polymerization initiator migrates to the surface of said fiber and said monomer penetrates into the interior of the fiber so that said hydrophilic polymer is formed both in the interior and on the surface of the fiber.