Elastic Recovery
The tendency of a paper or board material to return partially to its original flat shape after being folded or embossed acts as a measure of elastic recovery. Springback occurs because the cellulose fibres retain some of their internal tension even after the deformation force is removed. This physical reaction must be accounted for during the design of packaging to ensure that folded flaps stay closed and glue bonds remain intact.
Measurement Method
Measuring the degree of recovery typically involves calculating the angle of a fold after a specified holding time has passed. In a laboratory, a sample is bent to a fixed ninety-degree angle and then released to see how many degrees it moves back toward its original position. A higher angle of springback indicates a more resilient material that will put more stress on adhesive seals or mechanical locks in a finished box.
This value is influenced by the moisture content of the board and the direction of the grain relative to the fold.
Crease Optimization
Breaking the internal fibre structure in a controlled way allows the board to hold the new shape more permanently. The goal is to reach a state where the material is pliable enough to fold without cracking the outer surface.
