The width-related bending stiffness S describes the resistance of a specimen to bending. In the elastic deformation range, it is the product of the modulus of elasticity E valid for bending and the area moment of inertia I of the sample.

The bending stiffness is an important parameter for the further processing of paper and board. The stiffness or flexibility of the paper can have a detrimental effect on processing operations in packaging machines and lead to malfunctions.

The determination of the width-related bending stiffness S is carried out, among other things, according to DIN 53121, the two-point method.

For this, the specimen clamped at one end is stressed at a distance l by a force F acting perpendicular to the surface of the specimen. The tests are carried out with a clamping length of 50 mm and a bending angle of 5°. The specimen width is 38 (± 0.2) mm. 10 individual values are determined per test direction, 5 measurements each against the upper side and 5 measurements against the lower side, and an average value is calculated from these. The bending stiffness is given in Nmm.