expected to increase water uptake of composites prepared therefrom such an effect would result in lower wet glass transition temperatures and lower wet compression strength the surface of such microfibers may be rendered hydrophobic by treatment with a coupling agent such as 3 glycidoxypropyltrimethoxysilane or 2 3 4 epoxycyclohexyl ethyltrimethoxysilane in addition to forming a hydrophobic microfiber surface use of such compounds as coupling agents frequently aids compatibility with the matrix resin the coupling agent may be added to the microfibers by conventional techniques i e by applying 1 to 10 percent preferably 2 to 5 percent by weight of coupling agent to microfibers dispersed in a suitable solvent alternatively the coupling agent may be added to the microfiber premix if the microfibers are added directly to the resin rather than utilizing a premix the coupling agent may be added directly to the resin also in table iii the results of various impacts on composite panels prepared from a resin system containing microfibers treated with 4 percent by weight relative to microfiber weight of the coupling agent 3 glycidoxypropyltrimethoxysilane are compared with panels prepared from the same system but without microfibers the resin is the same resin as in example.