The potential of an externally applied holding pressure to produce (high density) RRIM parts was studied utilizing a mold with shear edges and a modified injection molding clamping unit. Surface quality, mechanical properties and demolding characteristics of the resulting parts are improved. The degree of nucleation gas used can be greatly reduced; reliability and reproducibility of the process are increased. Using BAYFLEX 150-IMR (polyurea) systems, extremely short cycle times can be realized. By selecting the correct combination of technology and chemistry, major steps towards automating RIM have been made, which means further cost advantages for RIM when compared to injection molding.