This article reports the synthesis of silica nanofiber/polydimethylsiloxane composites. Hollow silica nanofibers were synthesized through soft-template mediated synthesis using nitric acid catalyst and extensively characterized. Amorphous nanofibers were obtained by this method with mean diameter of 80 nm and length extending over several micrometers. Nanofibers were also prepared by varying the surfactant concentration and its effect on aspect ratio was investigated. Incorporation of these nanofibers into PDMS matrix was accomplished through in situ and ex situ preparative techniques. In situ prepared composites yielded maximum improvement in properties with 120% improvement in tensile strength, 175% improvement in room temperature storage modulus and 190 degrees C increase in temperature of maximum degradation ( (max)) even at low filler loading. Extent of nanofiller dispersion solely determined the property improvement of the composites. Nanofiller aspect ratio was also found to play an important role on the property improvement of the composites. Composite formation and hence property improvement were explained in depth in the light of free energy change and interaction parameter of the components of the hybrid material. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1005-1019, 2013