Recent interest in utilizing hydrogen fuel cell technology for automotive applications has lead to concerns regarding the durability of fiber reinforced polymer (FRP) composite materials. Automotive fuel cell power train systems must prove themselves as a reliable alternative to the combustion engines and automatic transmissions. The use of polymer composites in fuel cells to serve as manifolds is promising because of their high strength to weight ratio, and they do not corrode like metals manifolds. Composite materials designed for use in Polymer Electrolyte Membrane (PEM) Fuel Cells are exposed to very high humidity environment and operated at elevated temperatures (~85°C). The susceptibility of fiber reinforced polymers to reduction in modulus, strength, and life in chemical environments has been well documented in the literature, especially at elevated temperatures. A chopped carbon fiber epoxy composite (Material A) and a chopped glass fiber epoxy composite (Material B) were exposed at 85°C to air, water, and a 50/50 water/antifreeze mixture, and periodically examined for tensile, compression, and flexural strengths at various temperatures. Following 2000 hours (83 days) of exposure, Materials A & B did not reach full saturation. Fatigue tests were conducted at various load levels and temperatures to determine their effect on cycles to failure, and carpet plots were generated. Blister formation in aged composites led to reductions in material properties as great as 25% to 75%. A mechanistic explanation was developed for the formation of blisters in the epoxy composite. Recommendations for material improvement and feasibility of material use for fuel cell manifolds and pressure plates were made. / Master of Science