In the previous two parts of this series of articles, the relations among the foaming conditions, microstructure, and impact properties of expanded microcellular polystyrene (EPS) were discussed. In this article, the effects of the foaming conditions and structure on the tensile properties of EPS were investigated. A systematic investigation was performed based on a statistical experimental design. Various processing conditions were used and a wide range of cellular structures was developed. Regression analysis was conducted on the data and expressions were developed to quantify the relationship between the tensile properties and the cellular structure. Foaming time and foaming temperature were the most important processing parameters influencing the tensile modulus and strength. The tensile modulus and strength increased with an increasing foam density, but they decreased slightly when the cell size increased. Two different approaches were used to develop models relating the modulus to the foam density of EPS. Both models fitted the experimental data quite well. (C) 2003 Wiley Periodicals, Inc.