Some technical remarks about ring binders and sales sheets
The standard format for ring binders containing DIN A4 sales sheets is 26 x 32 cm.
Following with the previous example, when designing ring binders to contain DIN A4 sales sheets, the following format is required:
26 cm. back cover + 0.3 cm. courtesy + 3 cm. spine + 0.3 cm. courtesy + 26 cm. cover = 55.6 cm. width x 32 cm. height.
This will be the format of our document in InDesign or Illustrator. But be careful, the bleeding area should not be the usual 3 mm, but 20 mm. This is due to the fact that the paper wrapping the binder's cardboard has to wrap the whole thickness of the cardboard and stick to it on the binder's internal side.
As for the papers that make up the binder, these are basically 2: lining paper and endpapers. Lining paper is the paper that covers the ring binder's external side, and it is essential to laminate it in order to protect the printing from being scratched during the ring binder's production process. Endpapers are the sheets covering the binder's inward sides.
The cardboard deserves a special mention, as it is the core on which the lining and endpapers are glued. Its usual thickness is about 2 or 2.5 mm.
If our ring binder is going to be printed only on the outside (i.e., printed liner and blank endpapers), the liner paper could be a 150g coated gloss or semi-matt, and the endpapers a 140g white offset. If, on the other hand, both the liner and the endpapers are going to be printed, then the same paper stock may be used for both (e.g., 150g gloss or semi matt coated, both laminated). The important thing to keep in mind is that the grammage of both types of paper (liner and endpapers) must be within a minimum of 135 g. and a maximum of 150 g.