Khuram asks,
I’m trying to understand the bending resistance of corrugated board and how it is affected by liner and fluted medium. Also, which paper property or properties does bending resistance of corrugated board relate and how.
This is an excellent question.
The answer is that it depends on the tensile strength of the liners and the caliper of thickness of the combined board. Tensile stiffness orientation is also important as is stretch or elongation properties of the liners.
— Ralph
askralph 
January 12, 2017 at 1:57 pm
One issue with bending resistance often over-looked is the fact that it is the liners, and not the medium, that contribute to this kind of strength. While Edge Crush (ECT) performance depends on both, the medium’s main contribution to stiffness is keeping the liners a uniform distance apart.
Too much medium for too little liner (or vice-versa) means your constructions are out-of-balance. Your ECT won’t notice this weakness, but your bending resistance will. Related issue: While corrugator crews dislike unbalanced constructions, heavier constructions trend better Box Compression (BCT) with heavier liners on the inside (SF), but… if you test this idea with empty boxes in the lab you may notice a loss of BCT. This is because the panels of empty boxes typically deflect inwards with compression while filled boxes in a warehouse bulge out.
February 22, 2017 at 12:32 pm
Bending stiffness for corrugated board is well approximated to a few percent by the sandwich beam formula which has bending stiffness = ((liner tensile stiffness) x (board caliper squared))/2. So the medium only serves to increase board caliper but does not contribute to bending stiffness. Tensile stiffness here is the liner CD elastic modulus times the liner caliper. To increase bending stiffness through process, liner tensile stiffness is increased through higher density attained by a combination of wet pressing and refining.