Emanuele Parodi, Leon E. Govaert and Gerrit W.M. Peters Materials Technology group, Department of Mechanical Engineering, Eindhoven University of Technology, P.O.Box 513, 5600MB Eindhoven, The Netherlands Over the past decade, engineering polymers, such as polyamide 6 (PA6), became more and more important in load-bearing applications. In this field, knowledge about life time and failure mode is particularly required, in this respect, two aspects can be investigated: 1) the product geometry may be changed in order to improve the product performance; 2) the processing conditions, that have a strong influence on performance. In this research, the influence of processing on the mechanical properties of Polyamide 6 has been studied, for both pure and nucleated grades. By changing processing conditions, it is possible to obtain different phase: a stable monoclinic form called α-phase (slow cooling), a pseudo-hexagonal mesophase called γ (faster cooling) and even fully amorphous samples (quenching). An accurate study of crystallization kinetics has been performed by Flash-DSC in order to characterize this rich polymorphism, more in particular TTT-curves (temperature-time-transformation) have been constructed. The influence of process parameters (such as mold temperature, injection speed, flow influence and cooling time) on mechanical properties have been investigated by tensile tests. Since PA6 has a strong hydrophilic character, the influence of hydration on mechanical properties has been investigated by conditioning samples in different relative humidity and consequently testing (tensile test) in the same environment as conditioning.