Grain - The direction in which the paper fiber lies.
Grain direction - The dominant direction in which fibers in paper become aligned during manufacturing. Also called machine direction.
Against the grain - At right angles to the direction of the paper grain. Don't print books with the paper against the grain. Your books won't lie flat. Also called cross grain or across the grain.
With the grain - Folding or feeding paper into the press or folder parallel to the grain of the paper.
Recommended Reading: What is paper grain? - http://abookinaday.co.uk/tutorial-basics4.html
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