Machine direction

In the context of paper, the machine direction (direction of flow of pulp on machine, abbreviation: md) describes the arrangement of the pulp fibres in the finished product.

During paper production the fibres are released and arrange themselves parallel to the production direction of the paper web. As a result it is easier to bend the finished paper in one direction (with the fibre) than against the fibre direction. In paper used to make magazines and books, the machine direction must always be parallel with the spine, as otherwise the pages are very difficult to turn. Only in the covering materials for files and ring binders is it correct when in a transverse direction to the spine.

• Wide web (BB): The paper sheet lies wide in the paper web, DIN 6725, the short edge lies along the fibre length (also called short grain or grain short paper)
• Narrow web (SB): The paper sheet lies narrow in the paper web, DIN 16544, the long edge lies along the fibre length (also called long grain or grain long paper)