Polymer foams play an important role caused by the steadily increasing demand to light weight design. In case of soft polymers, like thermoplastic elastomers (TPE), the haptic feeling of the surface is affected by the inner foam structure. Foam injection molding of TPEs leads to so called structural foam, consisting of two compact skin layers and a cellular core. The properties of soft structural foams like soft-touch, elastic and plastic behavior are affected by the resulting foam structure, e.g. thickness of the compact skins and the foam core or foam density. This inner cellular structure can considerably be influenced by different processing parameters and the chosen blowing agent. This paper is focused on the selection and characterization of suitable blowing agents for foam injection molding of a TPO/TPC-blend. The aim was a high density reduction and a decent inner structure. Therefore DSC and TGA measurements were performed on different chemical and physical blowing agents to find out which one is appropriate for the used TPE. Moreover a new analyzing method for the description of processing characteristics by temperature dependent expansion measurements was developed. After choosing suitable blowing agents structural foams were molded with different types of blowing agents and combinations and with the breathing mould technology in order to get lower densities. The foam structure was analyzed to show the influence of the different blowing agents and combinations. Finally compression tests were performed to estimate the influence of the used blowing agent and the density reduction on the compression modulus. The combination of different blowing agents offered very homogeneous cell structures in combination with high expansion ratio. It could be shown that the foam structure can be influenced by the choice of the blowing agent or combination. In addition the mechanical compression tests revealed a mathematical correlation between the density, the skin layer thickness and the compression modulus so a prediction of the mechanical properties (compression modulus, flexibility) according to the density reduction of the TPE foam is possible.