Warp and weft: how a woven fabric holds together

Every woven fabric is built from two sets of threads. The warp runs lengthwise and is held under tension on the loom. The weft runs across, passing over and under the warp threads row after row. Because the warp has to survive that tension, warp yarns are usually stronger and more tightly twisted. That is why a woven fabric is often most stable along its length, and why patterns are cut with the grain in mind. The edges where the weft turns back are called the selvedge. They do not fray, and they tell you which way the warp runs: a useful clue when you are laying out a pattern. When you compare fabrics, ask which way the stretch and the strength go. The answer almost always comes back to warp and weft.