In this work, polyfunctional polyhedral oligomeric silsesquioxane (POSS) with glycidyl ether groups was physically blended with end-capped polyurethane (PU) to improve the mechanical strength of PU electrospun mats. It was found that not only the tensile strength was elevated, but also the elongation-at-break was greatly improved. Fourier transform infrared spectroscopy results suggested that no chemical reaction happened, and there was no hydrogen bonding between POSS and PU, but the mobility of the PU chains was restricted. Wide-angle X-ray diffraction patterns showed that POSS aggregated inside the PU electrospun fibers. Scanning electron microscopy observation showed apparent die-swelling, indicating that the elasticity of PU chains was enhanced. This was always the result of strengthened chain-chain interactions. From the experimental observations, it was speculated that a physical polymer-particle network was established through attachment of PU chains onto the POSS nanoparticles and embedment of PU chains inside the POSS aggregates, which results in the simultaneous improvements in strength and extensibility. (C) 2014 Wiley Periodicals, Inc.