Experimental investigation on the static and dynamic strength of false twist textured polyester yarns The mechanical properties of the yarns reflect their performance during the subsequent processes. In order to predict their performance, some testing indexes like tensile strength are used. Yet, these parameters cannot completely indicate the mechanical performance of the yarns in the spinning and subsequent processes, since they are static mechanical indexes. The aim of this study is to make a comparison between static and dynamic tensile strength values for the false-twist textured polyester yarns, and to investigate the effect of production parameter's, draw ratio and jet pressure on the strength values of the yarns. In the experiment, dynamic tensile tests have been conducted by CTT instrument to simulate the dynamic using conditions. Static tensile tests were measured by Zwick Z010 Universal Tensile Testing Machine and the test results were evaluated statistically. The dynamic strength was found approximately 10.4% lower than the static strength for all types of yarn.