Polyacrylonitrile (PAN) containing 10 wt.-% single-walled carbon nanotubes (SWNTs) exhibit a 100% improvement in tensile modulus and reduced thermal shrinkage and polymer solubility. A 40degreesC increase in glass transition temperature as compared to the control PAN fiber is also observed (see Figure). SWNT anisotropy has been observed using infrared spectroscopy.