ISO 5629:2017规定了使用共振法测定弯曲刚度的方法。 该方法仅为每个测试试件提供一个结果，但通常情况下，弯曲刚度值可能取决于材料的哪个表面形成由弯曲力产生的弧的内表面。 使用这种方法可以测量非常广泛的纸张和纸板的弯曲刚度。然而，对于某些材料，如下面列出的材料，测量的数值将与3.1中定义的弯曲刚度不完全相同: a） 多层纸和纸板，在测试过程中组件层可以单独移动； b） 具有明显卷曲的纸和纸板，特别是如果卷曲轴在试件的长方向上； c） 一些克重低于约40g/m2的软纸。 此方法不适用于瓦楞纸板。

ISO 5629:2017 specifies a method for the determination of bending stiffness using the resonance method. This method gives only a single result for each test piece tested, although in general, bending stiffness values may depend on which surface of the material forms the inner surface of the arc resulting from bending forces. The bending stiffness of a very wide range of papers and boards can be measured using this method. However, for some materials, such as those listed below, the measured numerical values will not be strictly identical with bending stiffness as defined in 3.1: a) multi-ply papers and boards in which the component plies can move separately during a test; b) papers and boards with appreciable curl, especially if the axis of the curl is in the long direction of the test piece; c) some soft papers with grammage below about 40 g/m2. This method is not applicable to corrugated boards.