Grain line

The grain line is the direction threads run in woven fabric, and matching it to the pattern markings keeps your costume hanging and moving correctly.

Every woven fabric is made of two sets of threads locked together at right angles. The lengthwise threads, called the warp, run parallel to the selvedge — the finished edge that came off the loom. The crosswise threads, called the weft, run from selvedge to selvedge. The grain line printed on a sewing pattern is almost always an arrow that should sit perfectly parallel to the selvedge, aligning your pattern piece with the warp. When you place a pattern piece off-grain, even by a small amount, the fabric can twist, pull, or drape in a direction you did not intend. A skirt might spin around your body during wear, a sleeve might pucker at the seam, or a shaped bodice panel might stop lying flat. Cutting on the grain line is one of the simplest ways to save yourself extra fitting work later, which is part of why checking the grain is standard practice before you cut your mock-up fabric too.