Samples of DuPont 7A and 7C Teflon (PTFE, poly(tetrafluoroethylene)) were tested in tension at strain-rates between 2 X 10(-4) and 0.1 s(-1) land temperatures between - 50 and 150 degrees C. Additionally, using a Hopkinson bar, a temperature series was undertaken in tension between -50 and 23 degrees C at a strain rate of 800 s(-1). To investigate the small-strain response, strain gauges were used to measure axial and transverse strain allowing the Poisson ratio to be calculated. The effect of crystallinity was investigated using 7C material thermally processed to produce more amorphous material. As expected, the tensile mechanical properties of PTFE are significantly affected by strain-rate and temperature, but only to a limited extent by crystallinity. The Poisson ratio at small strains was found to differ in tension (approximate to 0.36) and compression (approximate to 0.46). Failure behavior and microstructure were correlated to temperature induced phase transitions. (c) 2005 Elsevier Ltd. All rights reserved.