Blends of nylon 6 and a silsesquioxane additive, aminopropyl isobutyl POSS (APOSS) were prepared containing 0-5% POSS by weight. APOSS was previously demonstrated by us to be an ineffectual additive at concentrations of more than approximately 3% by weight, lacking solubility and favorable interactions with the polymer matrix. Significant reinforcement was only obtained under the extreme confinement and orientation conditions induced by melt-spinning, under which it was suggested the APOSS might undergo forced-assembly into elongated, rebar-like reinforcement structures. In the present work, we show that while the structure-property relationships of these systems, measured by WAXS, DSC and Raman spectroscopy revealed there are no major changes in the chemical structure induced by molecular interactions, rheological and SEM investigations on the APOSS-polymer systems suggest that at temperatures above the APOSS melting point, solubility and dispersion is slightly enhanced. We also show that two conditions seem to be necessary for improvement of properties: i) A sufficient concentration of APOSS needs to exist in the system to diffuse in significant quantities into the matrix upon re-melting; ii) The remaining non-diffused APOSS agglomerates need to be below a critical size around 4 gm in diameter, which does not happen for concentrations above approximately 3%. (C) 2013 Elsevier Ltd. All rights reserved.