Nanocomposite fibers involve the concept of integrally dispersing nanosized particles of the second phase inorganic material into fiber forming polymers such as nylon or polyester. The material goal involves obtaining bi-phasic fibers with high mechanical stiffness and strength, electrical conductivity and/or enhanced other features such as thermal stability. Thus far, the main difficulties toward achieving nanocomposite fibers are: (1) the inability of obtaining large quantities of nanoparticles in a pure, un-agglomerated state and (2) obtaining a uniform, intimate dispersion of single entity nanoparticles in a fiber polymer matrix. These problems have been approached in the context of studying the properties of experimentally prepared nano-silica reinforced fibers and attempts to prepare carbon nanotube, CNT, containing fiber material. Modulus and tenacity tests on experimentally prepared nanosilica filled PET (polyethyleneterephthalate) fibers showed the silica nanoparticles reduced the modulus and tenacity (tensile strength) of the filled PET fiber materials. DSC and shrinkage studies on nano-silica/PET fiber show that polymer crystallinity is influenced by the presence of the silica nano-particles. Heats of melting are found to increase as the filler loading increases. In further shrinkage studies, the “shrinkage modulus” of these nanosilica/PET fibers was found to increase by the addition of silica nanoparticles. Attempts to prepare nylon reinforced CNTs (multi-wall) from a commercially available CNT/nylon resin “concentrate” failed due to the poor melt dispersion processing of the blended polymer. Only very weak CNT reinforced nylon fibers could be prepared.