The effect of twist on the performance of polyethylene naphthalate, dimensionally stable polyester and high-tenacity polyester cord yams has been studied. It is observed that the twist has a very important effect on the tensile properties, creep properties and fracture mechanism. An increase in the twist level increases breaking elongation and creep rate but decreases breaking strength. Breaking mechanisms are also affected by the twist level. However, it is found that the material has the most important role on the cord performance.