The use of nanoparticles, including surface-modified silica and calcite nanoparticles, as processing aides for pultrusion is described. The methods include combining a resin system containing a resin and the nanoparticles with continuous fibers, pultruding this combination, and at least partially curing the resin. The methods are suitable for use with a wide variety of resins and fibers, and may be used to reduce the pull-force at a fixed fiber volume loading, increase the fiber volume loading, or both. Pultruded parts made by these methods and pultruded parts with high volume loadings of fibers are also described.