Hairpin windings are becoming current/next generation solutions for traction motors of electric vehicles due to inherently reduced DC power losses and improved heat dissipation capability compared with random windings. Copper-based conductor has been widely accepted as default option for hairpin windings. Meanwhile, aluminum remains a popular conductor material based on its light-weight characteristic and flexibility in manufacturing. In this paper, both copper and aluminum conductors will be evaluated based on specific hairpin winding layout applied in design of a 150kW, 18000rpm traction motor. Influences of conductor sizes on machine performance and power losses will be investigated for these two winding materials by 2D FEA of parametrized machine topology. It is interesting to find that by bringing this "old-fashioned"comparison back to stage, aluminum conductor might be promising candidate for hairpin windings due to reduced AC losses, easier preforming and welding process and much reduced raw material costs.