Machine-made paper has a grain: most fibres settle parallel to the direction the wet pulp travelled along the machine. A sheet folds cleanly, bends easily and swells least along that direction. Fold across it and the crease cracks, the sheet fights you, and a finished book warps as the room's humidity changes.
Four bench tests
- Bend. Curl the sheet loosely one way, then the other. It offers less resistance when bending parallel to the grain.
- Tear. Tear a scrap in both directions. The tear runs straight along the grain and wanders across it.
- Water. Dampen one side of a small square. It curls into a tube, and the tube's axis runs with the grain.
- Nail. Draw a thumbnail and forefinger along each edge. The edge cut across the grain ripples; the edge along it stays smooth.
Reading a paper label
Mills describe stock as long grain (grain parallel to the long edge) or short grain, or underline the grain-parallel dimension. Conventions differ between suppliers, so test a sheet anyway.
Office copier paper is nearly always long grain. That is why an A5 pamphlet folded from A4 cracks along its spine: the fold halves the long edge, so the grain crosses it. For a single-fold section buy short-grain stock, or start from a larger sheet and fold twice. The calculator below checks this for any sheet.