What is paper grain direction? Long grain, short grain, folding and binding

When the fibres run parallel to the long edge of the sheet the paper is long grain; parallel to the short edge, short grain. Suppliers usually show it in how the size is written or with a mark: 700×1000 and 1000×700 are not the same sheet, the grain runs the other way.

When you order, ask for the grain direction as well as the sheet size; two papers of the same weight and size can arrive with different grain.

With no label, a few simple tests tell you:

Paper folded with the grain folds cleanly; folded across the grain, especially heavy paper and board, it cracks and shows a white line at the fold. That is when a crease line is needed.

In books and magazines the grain should run parallel to the spine. Across the spine, pages are hard to open, try to close themselves and the spine waves over time.

Paper grows or shrinks as it gains or loses moisture, and much more across the grain than along it. In offset printing, if the sheet changes slightly between colours, the colours no longer register exactly.

That is why paper is left to acclimatise in the pressroom before printing, and many presses prefer the grain parallel to the cylinder. What suits depends on the press and the job; asking the operator is the safest route.

The folding direction, the spine and the press preference sometimes pull against each other. Decide first which matters most: the fold on a heavy cover, the spine on a book, registration on a thin multi-colour job.

Then work out how many pieces come out of the parent sheet, and the waste, with the grain held in that direction. A cut that looks cheaper but turns the grain the wrong way comes back later as a cracked cover or a book that will not open.