Thermoplastic polyurethane (TPU) is one of the most widely used and versatile thermoplastic materials. TPU foams have been extensively applied in various industries including the furniture, automotive, sportswear, and packaging industries. In this study, two methods of producing highly expanded TPU injection molded foam were investigated: (1) microcellular injection molding (MIM) with N-2 as a blowing agent, and (2) a novel gas-laden pellet/MIM combined process with N-2 and CO2 as co-blowing agents. Two designs of experiments (DOEs) were performed to learn the influences of key processing parameters and to optimize foam quality. By using N-2 and CO2 as co-blowing agents, a bulk density as low as 0.20g/cm(3) was successfully achieved with a hysteresis compression loss of 24.4%. POLYM. ENG. SCI., 55:2643-2652, 2015. (c) 2015 Society of Plastics Engineers