Nowadays, polymeric foams have attracted special attention in scientific and industrial societies due to their unique properties such as high strength to weight ratio, excellent thermal-insulation, sound-insulation, and good mechanical properties. One of the main goals of the studies of polymeric foams is to increase the cell density and aligning with it, is to reduce the cell size of these materials. Researchers have shown that the extraordinary properties of polymeric foams such as superior thermal-insulation can be achieved by increasing the cell density/ decreasing the cell size. In this regard, firstly the most important processes for the production of polymeric foams (batch, extrusion, and injection molding processes) were studied in the present research. Then, cell nucleation stage as the most important process for achieving high cell density/ low cell size is studied in details. In the following, the most important researches in the field of polymeric foams were introduced in which, the highest cell densities/ lowest cell sizes were achieved. The investigations show that the most significant results (highest cell densities/ lowest cell sizes) are belonging to the batch process. Also, the use of nucleating agents, increasing the solubility of blowing agent into the polymer, and the use of nanoparticles are the most efficient solutions in order to achieve microcellular and nanocellular structures.

Polymeric foams are one of the best candidates for thermal insulation. Accordingly, to investigate the thermal insulation properties of polymeric foams has attracted the attention of scientific communities in recent years. In this study, optimization of thermal insulation properties of polymeric foams is performed from solid and radiation thermal conductivities points of view. In this regard, a theoretical model based on cell size and foam density is developed. The results of the developed theoretical model are verified in comparison to various experimental results. Based on the results, the error of the theoretical model is lesser than 5%. Decreasing the foam density increases and decreases the solid and radiation thermal conductivity, respectively. Also, the radiation thermal conductivity is decreased by reducing the cell size. Response surface method (RSM) is applied in order to optimize the solid and radiation thermal conductivities. The results illuminate that the foam density of 23.5 kg.m^-3 and cell size of 53 μm are the optimum conditions. At the optimum conditions, both of the solid and radiation thermal conductivities are lesser than 3 mW/mK. According to the results, the data obtained from developed theoretical model and RSM are in a good agreement. The total thermal conductivity is 30 mW/mK at optimum conditions which is a desirable value at aforementioned cell size range.