A high temperature creep measuring apparatus capable of operating at different stress levels over a wide range of temperatures and humidities was built. The apparatus was used to investigate creep behaviour of nylon6.6 tyre cords, under isothermal and non-isothermal (cyclic) operating modes. Under both operating conditions, cords exhibited instantaneous extensions on loading followed by steady creep over time with an eventual failure. Increasing operating temperature accelerated creep rate and reduced creep failure time. At non-isothermal operating temperatures, the cords exhibited approximately 5-7 times longer creep lives than at steady state isothermal operating temperatures.