Blends of nylon 6 and a silsesquioxane additive, aminopropyl isobutyl POSS containing 2.5% POSS by weight, were melt-compounded with different process conditions in order to test a previously proposed mechanism for reinforcement of PA6 by POSS. In this work, we proposed that above the POSS melting temperature of 267 degrees C POSS becomes partially soluble in the nylon 6 matrix, leading to smaller domains upon cooling, and the remaining nondiffused POSS agglomerates need to have an acceptable size distribution, typically 16 mu m(2) or less in area. In this work, we test this hypothesis by producing blends with POSS existing as phase-separated aggregates of even smaller size than before and processing them under various thermomechanical conditions. Although there were no significant differences in the morphology and mechanical properties between the different extruded samples, the results from the spun fibers present significant improvements in tensile properties relative to previous reports. Our results suggest that in order to maximize the tensile strength of melt spun fibers, the extruded blends should be processed at temperatures above the POSS melting temperature and at intermediate shear rates, since these conditions lead to lower debonding between POSS particles and the matrix, and smaller average particle size. POLYM. ENG. SCI., 55:1580-1588, 2015. (c) 2015 Society of Plastics Engineers