The stress-strain characteristics of PTFE under uniaxial tension and compression have been measured at various temperatures. A new nite element analysis procedure using MARC is presented, which can simulate the diVerent properties of PTFE from tension and compression data. This method is based on using the maximum principal stress value at the integration point of each element to de ne whether the element is under tension or compression at each increment, then using subroutines to specify the material properties. A positive value indicates a state of tension and a negative value indicates compression. It has been found that the nite element analysis results are in good agreement with those from experiment. Finally, a PTFE rotary seal was modelled using this new method, and results were obtained incorporating stress and lip loads of the rotary seal, with diVerent temperature eVects.