By the continuous recording of the expansion process of chemically blown rubber materials, a new method for the characterisation of sponge rubber compounds is introduced. In contrast to the classical proceeding by means of oscillating die curemeters with coupled normal force dynamometer, this testing method provides a concrete mapping of the expansion process. Thus, the interaction between the vulcanization and the decomposition of the blowing agent is estimated not the single reactions itself. This overall rating allows an exact evaluation of the influences of the compound rheology and the kinetic of vulcanization and decomposition reaction on the reduction of the sponge density. The first investigations presented within this contribution show that different process parameters and the variation of the compound formulation are very easy to distinguish. The possibility of the matching of the different influences of the compound, the process and the part geometry is an essential advantage compared with the state of the art.