Nylon 11 coatings filled with nominal 0-15 vol % of nanosized silica or carbon black were produced using the high velocity oxy-fuel combustion spray process. The scratch and sliding wear resistance, mechanical, and barrier properties of nanocomposite coatings were measured. The effect of powder initial size, filler content, filler chemistry, coating microstructure, and morphology were evaluated. Improvements of up to 35% in scratch and 67% in wear resistance were obtained for coatings with nominal 15 vol % contents of hydrophobic silica or carbon black, respectively, relative to unfilled coatings. This increase appeared to be primarily attributable to filler addition and increased matrix crystallinity. Particle surface chemistry, distribution, and dispersion also contributed to the differences in coating scratch and wear performance. Reinforcement of the polymer matrix resulted in increases of up to 205% in the glass storage modulus of nanocomposite coatings. This increase was shown to be a function of both the surface chemistry and amount of reinforcement. The storage modulus of nanocomposite coatings at temperatures above the glass transition temperature was higher than that of unfilled coatings by up to 195%, depending primarily on the particle size of the starting polymer powder. Results also showed that the water vapor transmission rate through nanoreinforced coatings decreased by up to 50% compared with pure polymer coatings. The aqueous permeability of coatings produced from smaller particle size polymers (D-30) was lower than the permeability of coatings produced from larger particles because of the lower porosities and higher densities achieved in D-30 coatings.