Corrugated fiberboard is a material consisting of afluted corrugated sheet and one or two flat linerboards. It is made on "flute lamination machines" or "corrugators" and is used in the manufacture of shipping containers, consumer packaging, corrugated boxes, headers and many many many more things.
Like the with all paper and chipboard, corrugated cardboard has a corrugation direction which corresponds to the direction the waves follow, relative to a sheet or roll. The reason why this is relevant is that scoring and cutting against or with the corrugation with gives added strength or not and will allow for easy folding or not. Generally speaking you look to add structure to a box by scoring for folds against the corrugation direction.
No one accused the thickness logic to be easy - so the following is provided for your viewing enjoyment....... please don't ask us why C at it's relative thickness level is between B and E.
|Flute Type||Flutes per linear foot||Flute thickness (in)||Flutes per linear meter||Flute thickness (mm)|
|A flute||33 +/− 3||3⁄16||108 +/− 10||4.8|
|B flute||47 +/− 3||1⁄8||154 +/− 10||3.2|
|C flute||39 +/− 3||5⁄32||128 +/− 10||4.0|
|E flute||90 +/− 4||1⁄16||295 +/− 13||1.6|
|F flute||125 +/− 4||1⁄32||420 +/− 13||0.8|
While we can and often do work with all the above thicknesses, the bulk of the custom packaging industry and us works in F, E and B.
You can find more information on corrugated cardboard here.