This work identifies the necessary attributes of variable temperature cure epoxy-based prepreg systems as they relate to high performance prepreg systems capable for composite repair. Model polyetherimide epoxy blend resins were developed and hot-melt impregnated into woven carbon fabric and compared with a commercial prepreg system. It was found that when the PEI content was increased from 0 to 14 wt% in the base resin of the prepregs, the G(IC) and G(IIC) fracture toughness increased by over 70%. The fracture toughness was found to be similar when the model prepreg was cured at either 121 degrees C or 177 degrees C, a result of only a 9% difference in conversion and complete phase separation of the PEI at both cure temperatures. Void content in vacuum cured laminates were found to decrease as the PEI content was increased because of a large quantity of resin in the interstitial areas between the longitudinal and transverse tows. A comparison of the model and commercial prepreg system demonstrated many similarities and some significant differences. For example, the commercial prepreg had a 15% difference in conversion when cured at 121 degrees C versus 177 degrees C and very little PEI phase separation after both cure cycles. As a result, a significant difference in G(IIC) for the commercial prepreg was observed for the two cure temperatures.