In this study, the finite element method was used to investigate the influence of screw speed, entering peroxide distribution, pressure-to-drag now ratio, and channel geometry on the mixing characteristics of steady non-isothermal reactive flaws. The reaction considered was the peroxide-initiated degradation of a polypropylene resin in the metering zone of a single-screw extruder. The predicted average degree-of-freedom profiles from the simulations largely conformed to expectations. The average flow efficiencies for all runs were found to vary little along the channel length, remaining at values close to that for two-dimensional flow. No significant effect of either screw speed or peroxide distribution was found on the now efficiencies. However, both the pressure-to-drag flow ratio and the channel aspect ratio were found to have significant influences.