Studies were made of various factors affecting the structures and properties of high-density polyethylene (HDPE)/natural rubber (NR) foam such as heating time, blowing agent loading, HDPE/NR ratio, cross-linking agent loading, and ratio of HDPE/NR at a fixed cross-linking agent loading. The objectives were to gain insight into the foaming in the production process and to control foaming process for the manufacturing of good quality HDPE/NR foam. Preparation of the HDPE/NR foam, comprises basically of a high-density polyethylene, natural rubber, epolene wax, a chemical blowing agent, and a cross-linking agent. The HDPE/NR blends were prepared on a two-roll mill. Subsequently, foamed structures of the blends were obtained by a single stage compression molding. The results showed that the suitable heating time in this foaming process was 20 minutes. The HDPE/NR ratios had a significant effect on the mechanical properties and cell structure of HDPE/NR foams. At high ratio of HDPE/NR blend, the cells shape were distorted and the lower mechanical properties occurred. Adding the cross-linking agent could improve hardness and tensile strength. The average cell size decreased with increasing cross-linking agent loading. The suitable cross-linking agent loading for 30 pphp the blend containing NR was 0.6 pphp cross-linking agent
