weft

The weft is the yarn that runs perpendicular to the warp in woven fabric. While the warp threads are held under tension on the loom and run lengthwise down the cloth, the weft is inserted horizontally across them, interlacing to create a stable structure. On a loom, the weft is wound onto a bobbin or shuttle and passed back and forth through the shed, the opening created when warp threads are lifted and lowered by the harness.

Weft yarns are typically wound at lower tension than warp because they do not bear the stress of the loom's tension system. This means weft can use yarns that are slightly weaker or more delicate without breaking, and it often uses different fiber content than the warp. Many fabrics employ a heavy warp with a lighter, cheaper weft, or they use the same yarn for both but in different counts. The spacing and tightness of weft insertion directly control the fabric's weight, drape, and durability.

Weft insertion methods

On shuttle looms, the weft travels in a wooden or plastic shuttle that is thrown or picked across the width of the fabric. On modern air jet and water jet looms, the weft is inserted by a stream of compressed air or water, allowing much higher speeds. Rapier looms use rigid or flexible rods to push or pull the weft across. Each method affects the quality of the weave and the types of yarn that can be used. Jet looms, for instance, cannot handle very delicate or floppy yarns.

Weft defects are a major quality concern in weaving. Missing weft, where a pick fails to cross the entire width of the fabric, creates a thin or open place in the cloth. Weft breakage slows production and can trigger loom stops if not caught early. Uneven weft tension causes bands of tighter and looser weave that show as visible faults in the finished cloth. Most looms today use electronic weft detection sensors to identify these faults and pause the loom before damage accumulates.

The term weft comes from Old English and is related to the word weave itself. It is also called the fill or woof, especially in older texts and in some regional traditions, though weft is the standard modern industrial term. Understanding the relationship between warp and weft is essential for anyone specifying or troubleshooting woven textiles, because changes to weft selection alter both how the fabric feels and how it performs in end use.