Method for determining normal and shear stress-correlated material parameters, making use of a biaxial measuring device, which comprises a frame for tensioning a flat sample of a material which is soft under bending and shear forces on four sides, and a plurality of drive units (3a, 3b) for the imposition of normal and shear stresses onto the sample, wherein each drive unit is coupled to only one of the four sides of the sample, and the biaxial measuring device comprises an optical measuring device, which is operatively connected to a data-processing unit, comprising the steps a) applying a predefined character grid on the flat sample, of which the orientation can correlate with the orthrotropic directions of the sample or is irregular, and tensioning of the sample corresponding to its orthrotropic directions in the frame, b) detecting a first data set, which describes the first position of the character grid, by means of the optical measuring device and sending of the detected data to the data-processing unit, c) simultaneous imposing of predetermined normal and shear stresses onto the sample by means of the plurality of drive units (3a, 3b), thereby transforming the sample into a deformed state and changing the position of the character grid, d) detecting a second data set, which describes the second position of the character set, by means of the optical measuring device and sending of the second data set to the data-processing unit, e) determining a relative position change of the character grid by correlating the detected first and second data sets, and from this, by means of the data-processing unit, determining the relative shear and a present distortion state of the sample, f) from the shear and the present distortion state of the sample, determining of a deformation equilibrium of the deformed state of the sample, wherein the deformation equilibrium correlates to the material parameters, and g) from the deformation equilibrium, calculating and issuing of the material parameters, characterised in that h) the sample is coupled on each of the four sides in each to several of the drive units (3a, 3b), and i) in step c), the drive units (3a, 3b) at the frame can be displaced on each of the four sides separately from one another, wherein the sample is extended not only in two directions, but is simultaneously also transformed into a symmetrical distorted rhomboid or an unsymmetrical distortion state. a) applying a predefined character grid on the flat sample, of which the orientation can correlate with the orthrotropic directions of the sample or is irregular, and tensioning of the sample corresponding to its orthrotropic directions in the frame, b) detecting a first data set, which describes the first position of the character grid, by means of the optical measuring device and sending of the detected data to the data-processing unit, c) simultaneous imposing of predetermined normal and shear stresses onto the sample by means of the plurality of drive units (3a, 3b), thereby transforming the sample into a deformed state and changing the position of the character grid, d) detecting a second data set, which describes the second position of the character set, by means of the optical measuring device and sending of the second data set to the data-processing unit, e) determining a relative position change of the character grid by correlating the detected first and second data sets, and from this, by means of the data-processing unit, determining the relative shear and a present distortion state of the sample, f) from the shear and the present distortion state of the sample, determining of a deformation equilibrium of the deformed state of the sample, wherein the deformation equilibrium correlates to the material parameters, and g) from the deformation equilibrium, calculating and issuing of the material parameters, h) the sample is coupled on each of the four sides in each to several of the drive units (3a, 3b), and i) in step c), the drive units (3a, 3b) at the frame can be displaced on each of the four sides separately from one another, wherein the sample is extended not only in two directions, but is simultaneously also transformed into a symmetrical distorted rhomboid or an unsymmetrical distortion state.