sley

The sley is a fundamental specification in weaving that describes how tightly the warp threads are packed across the loom. It is expressed as the number of warp ends per inch of cloth width, typically ranging from 20 to 200 ends per inch depending on the fabric type. A fabric woven at 80 sley, for example, has 80 individual warp threads in every horizontal inch of finished cloth.

The sley directly controls cloth density and hand feel. Fine fabrics like broadcloth or poplin use high sley counts, often 120 to 160 ends per inch, producing tight, smooth cloth with good drape and wrinkle resistance. Coarser goods like canvas or heavy shirting may run 40 to 80 sley. The sley count is set during loom setup by selecting the appropriate reed, a comb-like component that separates and guides warp ends as the loom operates.

Setting and Measuring Sley

The reed itself is specified by two numbers: thread count and dent size. A 100-dent reed has 100 openings per inch; how many warp ends are threaded through each opening determines the final sley. Threading 2 ends per dent in a 100-dent reed yields 200 sley. This modular approach allows mills to achieve different sley values without replacing equipment. Weavers count sley by measuring finished cloth with a linen tester or by calculation from known warp thread counts and loom settings.

Sley affects more than appearance. Tight sleys require finer warp yarns and create higher tension on the loom, demanding more frequent thread breaks and higher energy consumption. Loose sleys allow heavier yarns and faster loom speeds but produce weaker cloth. Mills balance these trade-offs based on end-use requirements: apparel demands refined hand and appearance; industrial fabrics prioritize durability and production speed.

The term derives from the Old English slae, meaning to separate or divide, reflecting the reed's core function of dividing and organizing the warp. Sley is sometimes called picks per inch or warp density in casual speech, though picks per inch properly refers to weft, not warp. Confusion between these terms is common but creates specification errors, so precision in use matters on the mill floor.