The water absorptivity of corrugating medium is measured by dropping a drop of water on the surface of a specimen and determining the time in seconds for the drop to be completely absorbed as evidenced by the loss of sheen.

This method is applicable to corrugating medium as it is commercially produced by all processes. It is generally applicable to relatively unsized (water leaf) containerboards. It may not be applicable to more highly sized boards or to grades produced in different grammage (basis weight) than those normally used in corrugating medium.

The precision and repeatability of test results are dependant on the grade and manufacturing process. Use caution when making comparisons between samples that differ significantly in basis weights or manufacturing processes.

Aging effects on the absorptivity of corrugating medium made of recycled fibers have been shown to be negligible. However, this is not true for medium with virgin fibers. See Appendix A.

Due in part to the uniqueness of medium, various alternate methods are available for evaluating water absorption. These alternate methods are cited in Section 9 Additional Information.

Some producers test absorptivity of corrugating medium to know that it has the proper receptivity to the corrugating adhesive, which is an aqueous suspension of starch, for proper adhesion in the corrugating process. The absorptivity may also relate to the way the medium can be steamed by the showers on the singlefacer and by the preconditioner.