Paper folding resistance

As one of the core indicators for measuring the mechanical properties of paper and paperboard, its precise definition is: under standardized test conditions (including specific temperature and humidity environments, specimen dimensions, folding pressure and speed parameters, etc.), using specialized folding endurance testing instruments (such as the Schopper folding endurance tester, MIT Folding Endurance Tester, etc.), to perform repeated folding operations on a paper specimen of specified dimensions until failure occurs. This value is measured in “double folds”—each complete cycle of “forward fold + reverse fold” counts as one double fold—visually reflecting the paper's ability to resist repeated folding damage.

Essentially, fold resistance is a composite measure of paper strength and flexibility. It is closely related not only to the length, bonding strength, and arrangement of internal fibers but also influenced by multiple factors including paper basis weight, thickness, moisture content, sizing degree, and added fillers or additives. Paper with longer fibers and tighter bonding typically exhibits superior tear resistance and flexibility, resulting in higher fold endurance values. Conversely, excessively high or low moisture content reduces fiber flexibility, thereby compromising folding endurance. This explains why folding endurance tests require strict control of environmental temperature and humidity (typically 23°C ± 1°C, relative humidity 50% ± 2%) to ensure accurate and comparable results.