A siloxane with hydrolyzable alkoxy groups in its side chains is found to attach to E-glass fibers as effectively as a trialkoxysilane. However, a hydroxyl-terminated poly(dimethylsiloxane), while interacting with the E-glass fibers from solution, is almost totally removed from the glass surface by subsequent washing with a variety of organic solvents. Diffuse reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy data are used to establish the interaction of such siloxanes with the glass surface, and the strength of such an interaction is indicated by the extent of removal of the adsorbed species after washing with various solvents.