Corrugated flutes and board calipers

Which flute you pick changes the thickness of the board, and the thickness of the board changes every allowance in the dieline. This is why the generator asks for it before it draws anything.

What a flute is

Corrugated board is a fluted paper medium glued between flat liners. The waves are the flutes. They act as a row of arches: they hold the two liners apart, resist crushing from above, and cushion whatever is inside. Take the flutes away and you have two sheets of paper.

• Single wall — one fluted medium between two liners. Most boxes.
• Double wall — two fluted mediums and three liners, usually two different flute profiles bonded together.
• Triple wall — three mediums and four liners. Industrial loads and pallet boxes.

The profile letters

Flute profiles are named by letter. The letters are historical rather than ordered, so they do not run in size order: A, C and B are the three classic profiles, largest to smallest, and E, F and N are the micro-flutes below them.

As a rule, the taller the flute the more cushioning and vertical stacking strength you get. The smaller the flute the flatter the surface, the better it prints, the more tightly it creases and the less bulk it adds to a folded blank.

Which one to pick

• General despatch, moderate weight. B flute. It is the default here because it is the default everywhere.
• Fragile or awkward contents. C flute, for the extra cushioning depth.
• A retail-facing box, or one with heavy print. E flute. The finer profile gives a flatter surface and much less washboarding through solid ink.
• A small carton-like box that still needs some rigidity. F or N micro-flute. Thin enough to crease cleanly and fold like cartonboard.
• Heavy, dense or exported goods. BC or AC double wall.
• Pallet-scale or industrial. Triple wall.

A double-wall code is read as its two component flutes. EB is an E flute bonded to a B flute: the fine E face takes the print, the B flute underneath does the work. BC is the general-purpose heavy grade.

If you are hesitating between two, the cheaper decision is usually to keep the flute and change the construction. Moving from 0201 to 0203 doubles the board across the top and bottom without changing grade at all.

Folding cartonboard and greyboard

Cartonboard is solid board, not fluted, and the trade specifies it by weight in grams per square metre rather than by thickness. The generator needs the thickness, so its board list pairs them.

Be careful with that pairing. Grammage and caliper are not the same property and the relationship is not fixed: a bulky board and a dense board at the same gsm can differ noticeably in thickness. If your printer has given you a caliper for the specific board they run, that number beats any table — type it in.

Greyboard is for rigid boxes, where the board is not folded but cut into separate pieces and wrapped.

Why the generator asks

Board thickness is not a cosmetic setting. It drives:

• The dimension allowance. Wrapping board around a product adds roughly one caliper to each internal dimension, and the outside is one caliper larger again. That is how the app converts between inside, crease-to-crease and outside readings.
• Slot width. The gap cut between adjacent flaps defaults to the board thickness, which is standard practice — the slot has to be wide enough for the adjacent flap to swing past.
• Corner clearances and tuck depths. Every fold has to wrap around the material, and every point where two folded panels meet needs room for both.

This is why a dieline that works perfectly on 0.4 mm cartonboard binds solid on 4 mm C flute. If a box will not fold up, check the caliper first. It is the answer more often than not.