The biaxial response of extruded PEEK films at conditions relevant to thermoforming has been investigated extensively using a combination of load-controlled (bulge test) and displacement-controlled (biaxial stretcher) experiments. Results from bulge testing yielded average and maximum strain rate ranges of 2.5-5 and 5-18 s(-1), respectively, across the forming temperature range. In-plane biaxial characterization highlighted the anisotropic nonlinear viscoelastic behavior of the films with strong dependence on the yield and strain hardening behavior on the temperature and strain history at conditions equivalent to the forming process. The combined approach to material characterization highlights the pros and cons of each test method, the complementary nature of the data generated, and the need to use both methods to have a complete data set for developing accurate material models and validated numerical simulations of thermoforming. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers