What paper grain direction should I fold along?

Always fold with the grain, never against it. Grain direction is the way the paper fibers naturally line up, and folding along that line gives you clean, professional creases.

• Folding with the grain produces smooth, crisp folds
• Folding against the grain causes rough, cracked edges, especially on coated and heavier stocks
• To find the grain, gently bend a blank sheet both ways. The direction that bends with less resistance is the grain

Test on a scrap sheet before committing your full run, and your folded pieces will look sharp instead of cracked along the crease.