regain
The amount of width a woven cloth grows by when the fibers swell, used to determine the width of the reed to use in weaving.
regain: cloth width expansion from fiber moisture
Regain is the increase in width that a woven cloth undergoes when its fibers absorb moisture and swell. It occurs naturally as yarns pass through the loom and after weaving, when the fabric encounters humid air or direct moisture. The weaver must account for this expansion by setting the reed width narrower than the desired finished width, so that the cloth reaches specification after moisture is absorbed.
The amount of regain depends primarily on the fiber content. Wool regains easily and predictably, typically around 2 to 5 percent of its dry width under standard humidity. Cotton regains less, around 1 to 3 percent. Synthetic fibers like polyester show minimal regain. Blended fabrics fall between their component fibers. The weaver must know the fiber type and the anticipated humidity environment to calculate the correct reed width accurately.
Regain affects both width and weight. As fibers swell, not only does the cloth grow wider, but it also becomes heavier because it has absorbed water. This weight gain can be significant in woolens. The moisture content stabilizes at standard regain, typically defined as the water absorbed at 65 percent relative humidity and 20 degrees Celsius, a condition used for testing and specification purposes across the textile trade.
Why it matters in the loom
A weaver who ignores regain will produce cloth that is too narrow when finished. If a customer specifies 60 inches finished width but the fabric is set into a 60-inch reed without regain allowance, the cloth will come off the loom at perhaps 57 inches, requiring correction or causing rejection. Conversely, overestimating regain leads to overwidth cloth that must be trimmed, wasting material.
Different dyes and finishes also influence regain slightly. Some sizing and chemical treatments can reduce the hygroscopic nature of fibers, while others enhance it. A dyed wool cloth may regain differently than an undyed sample of the same yarn. This is why mills often measure regain on samples prepared with the intended finishing process, not on raw fiber.