Various polymer surfaces were analyzed for reactivity toward 3-aminopropyltriethoxysilane (APTES). Results indicate that the method described here is useful as a general surface-selective modification technique for polar polymers such as polyesters, polyamides, polycarbonates, polyimides, cellulosics, polyacrylics, etc. X-ray photoelectron spectroscopy (XPS) showed an average of 10% silicon and nitrogen atomic concentrations at 75 degrees takeoff for all successfully modified surfaces. The APTES multilayers were subsequently hydrophobized with perfluorinated chlorosilanes giving 40% fluorine atomic concentration by XPS and 120 degrees/90 degrees (advancing/receding) dynamic contact angle averages. APTES modifications were successful in all solvents with the exception of protic solvents. On the basis of these and other observations, a new model for the reaction pathway is proposed. We propose the reaction proceeds by initial APTES adsorption (likely through hydrogen bonding by the amine) to the substrate, lateral bond formation, and subsequent multilayer formation. The model is thus analogous to silane multilayer formation on silica.