## 4 Conclusions  
Specimens sampled from the bottom of EPS boxes with a capacity of 3 kg were used in the uni-axial quasi-static compression test and flexure test, and EPS boxes with densities of 22 and 23 kg/m\({}^{3}\) were involved. The data obtained from the compression test were used as material parameters in the following FEM analysis simulating EPS boxes under stacking; the results of the FEM analysis were then compared with the results of the stacking strength test performed in this study. In addition, as one of the constraints for the future optimal design, the bottom strength of EPS boxes was examined. In the mechanical properties test, the compressive strength and flexure strength were primarily influenced by density. Roughly an 8% rise in compressive strength was observed in EPS23 compared to EPS22, and the initial modulus had around a 10-15% rise. However, the specimen's size and the preparation method had a minor influence on the compression and flexure tests. Specim size did not affect the compressive strength and tangent modulus in the compression test; there was only a 20% rise in the initial modulus of the compression test if specimens were 2 mm thicker, and it affected almost nothing in the flexure test. As for the method of preparation, around 2% higher stress was observed in the results of specimens cut with a hot wire in most test groups. The difference was not as distinct as in the compression and flexure tests when the boxes were tested as a whole. In the stacking strength test, with density increased by 1 kg/m\({}^{3}\), there was a 2.7% increase in load when breaking the box. The corresponding number was \(-\)10.3% for the bottom strength test. It is not necessarily that density affected the strength of EPS deeper in compression and flexure tests than in strength tests as a whole. The most plausible explanation is that EPS boxes with a density of 23 kg/m\({}^{3}\) used in whole-box tests were of inferior quality. An attempt to make the structure of the box lighter was also investigated in the stacking strength test and the bottom strength test. With 4 mm material shaved by a hot wire from the bottom, the rounding on the bottom edge was almost eliminated, whilst the walls were shorter, and this difference gave an 8.8% and 5.1% rise at 10 mm deformation in the stacking strength experiment and simulation, respectively. Meanwhile, the bottom strength decreased by 20.4% if 4 mm thick material was shaved off. This suggested that it was possible to consume less material and improve the stacking strength merely through topological modifications; however, bottom strength might be impaired. For now, the wall shortening that increased the critical force in buckling or the radius change of the foot corner could be the underlying cause of the improvement in stacking strength with the 4 mm material removed from the bottom of EPS boxes. The simulation results of the EPS boxes were in good agreement with the experimental results, indicating that the material parameters obtained from experiments and then included in the simulation material model were capable of delivering a satisfactorily accurate prediction. As mechanical properties could be varied to a remarkable extent if derived from the literature, for the accuracy of simulation, performing mechanical properties tests for the particular EPS is highly recommended. In future work on optimal lightweight designs of the box, the numerical model developed in this study will be an important tool. As for the method of preparing specimens, cutting with a table saw complied with the methods of specimen preparation suggested in ASTM D1621 and presented better results in conformance statistically. However, cutting with a hot wire was acceptable if the specimens' tension and compression sides were preserved as original surfaces, especially in a flexure test. Therefore, adopting the methods depends on specific demands. Additionally,to determine the safety factor of a brittle material in FEM analysis, a tensile test may be conducted.