This specification covers one type of glass cloth impregnated with a heat-reactive, thermosetting, solution-addition-type PMR-15 polyimide resin system, supplied in the form of continuous rolls of full width cloth or slit tape. This cloth has been used typically for structural laminates requiring high strength and heat resistance for long-term service up to 290 degrees C (554 degrees F) and short-time service up to 315 degrees C (599 degrees F), but usage is not limited to such applications.