The strength of a corrugated box begins with the material used. A corrugated sheet includes two primary components – linerboard and medium.
Linerboard refers to the flat paper that covers both sides of the corrugated sheet and the medium is the fluted or arched paper found between both sheet liners.
The flute, drugs when glued to the linerboards can resist bending and pressure from various directions. The most commonly used are “B-Flute”(used for die-cut boxes) and “C-Flute (used for RSCs).
The amount of virgin pulp fibers and the length of those fibers in a corrugated sheet significantly contribute to the strength of a box.
For example, the differentiation between a 200# test box and a 275# test box is that the second has more pulp fibers in its corrugated linerboard. The 200# test box is rated to hold up to 65 lbs. of box and contents while the 275# box can hold up to 95 lbs.