Paper is a material produced by compaction of the fiber. In papermaking, pulp fibers are oriented predominantly in the direction of operation of the paper machine. From the parent paper roll, the sheets are then cut in a way by this picture.
The sheets distinguished according to the direction of the fibers on strait-beam (SB) or broad-beam (BB) arcs.
BB - broad-beam: The fibers are parallel to the short side of the sheet.
SB - strait-beam: The fibers are parallel to the long side of the sheet.
What is it important to know which fiber path has a sheet of paper?
Paper properties differ in fiber paths. For example, under tension is paper stronger in fiber direction.
When printing, the paper extends proportionally with moisture soaking. In the direction of the fibers, the change in dimensions is less noticeable, while the paper stretches much more perpendicular to the direction of the fibers. This is important to know especially when printing multiple colors.
In bookbinding, it is important to respect the fiber path in the bending of the paper. The fiber must be oriented in the same direction as the bend. Otherwise it may break and crack in the bend.