Paper grain refers to the directional characteristic formed when plant fibers align with the direction of the machine during paper production. Simply put, it is the alignment direction of the fibers inside the paper.
During papermaking, diluted pulp is sprayed onto a continuously moving mesh screen. As water drains away, the long and thin plant fibers naturally align with the direction of the machine, forming the paper grain. The direction parallel to the fiber alignment is called "long grain" or "machine direction", while the direction perpendicular to it is known as "short grain" or "cross direction".
It is worth noting that the natural grain of paper is an absolute concept, which is different from the texture of embossed paper. Whether paper is long grain or short grain is a relative concept, depending on the paper size. If a full-size sheet is long grain, it will become short grain after being cut in half.
Long grain and short grain differ significantly in performance. Along the long grain direction, paper has higher tensile strength and better folding resistance; folds are smooth and less likely to crack. Meanwhile, the long grain direction is less affected by humidity and has good dimensional stability. The short grain direction, by contrast, tends to crack when folded, is sensitive to humidity changes, and easily expands or contracts.
In practical use, long grain is more suitable for applications requiring high strength and repeated folding, such as bookbinding, maps, and greeting cards. Aligning folds with the long grain greatly extends service life. In printing, matching the long grain with the cylinder axis also reduces registration errors. Short grain is often used in crafts where a natural torn edge is desired.
The simplest way to determine paper grain is by tearing the paper: tear from two adjacent edges. The direction that tears more easily and produces a straight edge is the long grain direction.
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