The method for stiffness measurement is outlined in several international standards. These standards describe cutting a sample of pre-determined size either from a sheet of virgin material or from a pre-formed carton blank.
The sample is gripped in jaws and rotated through a set angle, and the force transmitted through the sample is measured. This force is quoted in grams for comparative measurements or g/cm2 -an absolute value for the tested substrate. Some instruments may also quote the value in mN or mN/m2.