We report on a family of electrospun nano-composites, which are capable of altering their stiffness upon hydration. An electrospun mat of poly(vinyl alcohol) (PVA) was incorporated as the filler in a polymeric matrix consisting of either poly(vinyl acetate) (PVAc) or ethylene oxide-epicholorohydrin copolymer (EO-EPI). The tensile modulus of the EO-EPI-based composites was found to increase significantly upon incorporation of the PVA filler mat, while PVAc-based composites exhibited modulus enhancement only above the matrix glass transition. Materials based on the PVAc matrix and PVA electrospun filler exhibited a reversible reduction of the tensile modulus by a factor of 280 upon exposure to water. In contrast, composites comprised of a rubbery EO-EPI matrix and PVA filler showed a reduction of tensile modulus upon water uptake, but with incomplete restoration when dried. A systematic investigation revealed that the underlying mechanism of mechanical response is related to the matrix-filler interactions and filler crystallinity. The robust technique of electrospinning allows the tailoring of matrix-filler interactions in a new series of all-organic composites to achieve desired mechanical response upon exposure to various stimuli.