Warp, weft and twill

Warp and weft

A woven cloth is two sets of yarn at right angles. The warp runs the length of the bolt, held under tension on the loom. The weft is carried back and forth across it. The warp is usually the stronger, more tightly spun yarn, which is why a garment is cut with the warp running up and down the body — the direction that takes the most strain.

On a pattern that direction is the grainline, the long arrow on every piece. Cut off-grain and the garment twists and hangs wrong. Most of the care in laying out a pattern is keeping every piece on grain.

Twill

If the weft simply went over one warp and under the next, you would get a plain weave — canvas, muslin, most shirting. A twill offsets each row by one, so the weft goes over two or three warps and under one, and the crossings line up into a diagonal. Denim is a twill: the diagonal on the face is the warp yarn, and on the back you see mostly the weft, which is why the inside of a jean is paler.

Twill packs more yarn into the cloth than a plain weave of the same yarn, which is part of why it is durable, and the diagonal gives it a little more give.

Broken twill

A regular twill's diagonal runs one way, and a leg cut from it can slowly twist around itself as the cloth relaxes with wear. A broken twill reverses the diagonal every few yarns, so the surface reads as a fine zigzag and the twisting forces cancel. The cloth is a little flatter and more stable in a garment; it also fades more evenly, without the strong diagonal grain of a standard denim. Here it is used for pocket bags, where stability matters more than character.

Herringbone

A herringbone is a broken twill with a longer rhythm: the diagonal runs one way for a band, then the other, so the surface looks like a row of fish bones. It is stable like a broken twill and has a visible texture of its own. The Chore Coat is cut from a herringbone twill, and the same family of cloth lines the Foundry Jacket.

Why it matters

Weave decides how a cloth hangs, how it wears, how it fades and whether a leg twists. When a project says "twill", which twill is part of the reason it was chosen. The material pages name the weave alongside the weight.