This course provides the structure to property relationships of thermoplastic and composite foams. The crystal morphology (crystallinity, crystal size, crystal kind, crystal number, etc.), the cellular morphology (cell density, cell size, void fraction, uniformity, open cell content, etc.), and the composite structures (the fiber/platelet kind, the fiber/platelet aspect ratio, fiber/platelet orientation, the interface of fiber/platelet and matrix, etc.) affect various properties of the final products such as the thermal conductivity, the electrical conductivity, the mechanical properties, of various thermoplastic and composite foams. The mechanical properties (tensile properties, flexural properties, impact strength, etc.), the thermal conductivity (polymer conduction, gas conduction and radiation), and the electric conductivity are described as a function of the aforementioned structural parameters. The effects of the nano particles (carbon nanotube (CNT), graphene nano platelets (GNP), nanofibrils, etc.) on the properties are also discussed. Nanofibril compositess and their processing, structure characterization and property testing are also intensely discussed.