This part of IS0 6721 describes a flexural, nonresonance method for determining the components of the Young’s complex modulus E* of polymers at frequencies typically in the range 0,Ol Hz to 100 Hz. The method is suitable for measuring dynamic storage moduli in the range 10 MPa to 200 GPa. Although materials with moduli less than 10 MPa may be studied, more accurate measurements of their dynamic properties can be made using shear modes of deformation (see part 6 of IS0 6721). This method is particularly suited to the measurement of loss factors greater than 0,l and may therefore be conveniently used to study the variation of dynamic properties with temperature and frequency through most of the glass-rubber relaxation region (see IS0 6721-1:1994, subclause 9.4). The availability of data determined over wide ranges of both frequency and temperature enables master plots to be derived, using frequency/temperature shift procedures, which present dynamic properties over an extended frequency range at different temperatures.