The performance of copper alloy mold tool materials in injection molding has been examined with respect to cycle time, part quality and energy consumption using in-process monitoring techniques. A mold insert manufactured from conventional tool steel was compared to four identical inserts made from beryllium-free copper alloys with copper contents ranging from 85 to 96%. Injection molding trials using high density polyethylene and polybutyl terepthalate were performed using a highly instrumented injection molding machine. Results showed that copper alloy mold tools exhibited cooling rates up to 29% faster than conventional tool steel and that cooling rate was related to thermal conductivity of the alloy. Lower cycle times were achievable with copper alloy than for tool steel before part quality deterioration occurred. The results suggest that copper alloy tooling has the potential to achieve significant reductions in cycle time without detriment to the process or product quality. POLYM. ENG. SCI., 51:1837-1847, 2011. (C) 2011 Society of Plastics Engineers