Abstract: An in situ fiberization apparatus for continuously fiberizing belt shaped substrates by impregnation with fibrous material formed from fiber forming polymer solutions. The apparatus includes a belt substrate which is continually passed through a fiber forming solution at a constant rate. During passage of the substrate belt through the fiber forming solution, the apparatus provides continual oscillation of the belt. The oscillating or reciprocating motion of the belt substrate produces the conditions for flow-induced crystallization of fibers around and throughout the substrate material to thereby produce a fiber reinforced substrate.