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 penetrate through the sheet and wet the lower surface.
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.
Three alternative methods which can be performed in the same general time period with equal repeatability are listed in the Appendix. They do not give the same numerical results, but, in general, will rank the materials in the same order as the preferred method.
TAPPI T 432 "Water Absorbency of Bibulous Papers"; and TAPPI UM 596 "Water Absorbency of Non-Bibulous Paperboard" have been used to measure the water absorptivity of corrugating medium, but the study which led up to the development of this method indicates that they lack the repeatability of this method and most certainly take more time to conduct, especially on the more resistant samples.
