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In this paper, the most important results are presented and discussed from a multiyear interdisciplinary study directed toward the identification of the most suitable glass/polymer composite systems with the highest resistance to brittle fracture for high voltage composite insulator applications. Several unidirectional glass/polymer composite systems, commonly used in composite insulators, based either on E-glass or ECR-glass fibers embedded in either polyester, epoxy, or vinyl ester resins have been investigated for their resistance to stress corrosion cracking in nitric acid. The most important factors (fiber and resin types, surface fiber exposure, polymer fracture toughness, moisture absorption, interfacial properties, sandblasting) affecting the resistance of the composites to brittle fracture have been identified and thoroughly analyzed. It has been shown that the brittle fracture process of composite (nonceramic) insulators can be successfully eliminated, or at least dramatically reduced, by the proper chemical optimization of composite rod materials for their resistance to stress corrosion cracking.