The present invention is directed to an improved internal mold release system for the production of high density molded SRIM parts, i.e. molded parts having a density of from 1.3 to 2.0 g/cc. In particular, the process involves reacting a reaction mixture comprising an organic polyisocyanate and at least one organic compound containing isocyanate-reactive hydrogens in the presence of a catalyst and an internal mold release agent in a closed mold. The internal mold release agent is a compound corresponding to the formula: ##STR1## wherein R.sup.2 represents hydrogen, the group R.sup.5 --NH--CO--, or a C.sub.1 to C.sub.24 alkyl or substituted alkyl group, a C.sub.3 to C.sub.24 cycloalkyl or substituted cycloalkyl group, a C.sub.2 to C.sub.24 alkenyl or substituted alkenyl group, or a C.sub.6 to C.sub.24 aryl or substituted aryl group, andwherein R.sup.1, R.sup.3, R.sup.4 and R.sup.5 may be the same or different and represent a C.sub.1 to C.sub.24 alkyl or substituted alkyl group, a C.sub.3 to C.sub.24 cycloalkyl or substituted cycloalkyl group, a C.sub.2 to C.sub.24 alkenyl or substituted alkenyl group, or a C.sub.6 to C.sub.24 aryl or substituted aryl group,with the proviso that at least one of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is a C.sub.12 to C.sub.24 alkyl or substituted alkyl group, or a C.sub.12 to C.sub.24 alkenyl or substituted alkenyl group, and with the further proviso that substituent groups are inert toward isocyanate groups at temperatures of 100.degree. C. or less.