Before a box becomes a box, it is a flat sheet of board that the printer prints and cuts to shape. The dieline is the drawing of that sheet. It uses different line types to mark where the machine cuts the board and where it folds it, so both the designer and the printer work from it.
The dieline is usually supplied by the printer or the plant that makes the box, matched to the size and structure of the box. For a package with a custom shape, the structure has to be designed as well and checked with a sample that it holds together and can carry the product. For standard box shapes this step is simpler, as we start from the printer's ready template. On most projects we request the drawing in agreement with the printer, because they know which machine and what tolerance they work with.
Why it matters in the design
On a flat drawing it is hard to picture which surface ends up where on the folded box. The front and side of the box sit next to each other on the dieline, the top may even be upside down, and a badly placed text can end up in a fold or under the glue flap. That is why we always build the artwork on the dieline, and check it with a 3D visual and a printed, folded test.
The bleed also has to be marked on the dieline, meaning the strip up to which the artwork has to extend beyond the cutting line, so no white line is left at the edge of the box after cutting. Together with the crop marks and the prepress work, this decides whether the finished package will look the way it did in the visual.
Alongside the dieline it is worth settling the material early. A thick board or a corrugated box bends differently, and the artwork behaves differently at the folds than on a thin, glossy board. If the printer tells us in advance what material they print on, we can adapt the design to it, and the print proof holds fewer surprises.
For a product family we also watch the differences between the dielines. A larger pack size gets a box with different proportions, and the artwork has to work the same way on both sizes, so they appear as one series on the shelf.
