The thermal presssure coefficients of a neat, unfilled, epoxy resin and a 10 wt % POSS (polyhedral oligomeric silsesquioxane)-filled epoxy nanocomposite have been measured Using a thick-walled tube method. It is found that just below the glass transition temperature the thermal pressure coefficient is similar to 20%, smaller for the polymer composite containing 10% POSS than for the neat, unfilled resin. The thermal expansion coefficient and thermal pressure coefficient of the uncured POSS itself are also reported. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116:142-146, 2010