Fiberboard and Strength
A fiberboard’s strength is usually determined by the different weights of liner and medium used in its construction. These are commonly referred to in the industry by their basis weights (ex. 26#, 48#, 37#). The basis weight is the weight (in pounds), of 1000 sqft of either linerboard or medium. Different combinations of linerboard and medium are combined to meet the necessary strength requirements.
Historically, box strength has been measured using the Mullen test. This was calculated by determining the number of pounds per square inch required to break through the board.
The new standard of measuring a boxes strength is the Edge Crush Test (ECT). The ECT is a measure of the edgewise-compressive strength of a corrugated cardboard box. The ECT test is highly applicable because it is a good measure of the stacking strength of a given box design.
To test ECT a segment of fiberboard is compressed between two rigid plates pressed perpendicular to the direction of the flutes until a peak load is established. The calculation is measure in pounds per lineal inch of load bearing edge (lb/in), but is usually reported as an ECT value (ex. 26 ECT, 44 ECT).