Denim, and what happened to the weight

The working weight of denim sat between thirteen and fourteen ounces for most of the last century. Rigid, awkward for a fortnight, then shaped to whoever wore it. What hangs on a rail now is closer to ten ounces with elastane run through the yarn. That shift was not made in a design studio. It was made in a returns department.

Weight in denim is measured in ounces per square yard of finished cloth, and it is the most useful number on a swatch ticket. Fourteen ounces is a work fabric: dense, stiff off the roll, slow to break in and correspondingly slow to wear out. Twelve is the comfortable middle. Below ten and a half the cloth starts to behave like a shirting, draping rather than holding, taking its shape from the body underneath instead of imposing one. None of that is a question of taste. It is a question of how much cotton occupies a given area and how tightly it has been spun. The move downward was commercial. Trousers sold online carry a return rate that any buyer can quote from memory, somewhere between a third and a half depending on the market, and the reason given is almost always fit. Stretch narrows the range of bodies a single size has to fail. Two per cent elastane will absorb three centimetres of variation at the waist without complaint, which folds three sizes into one and takes several points off the returns. Against that, mill cost and hand feel are minor arguments. What is bought with those points is a fabric with a service life shorter than the cotton in it. Elastane is a polyurethane filament wrapped in cotton, and it degrades on a schedule of its own: heat from a tumble dryer, chlorine, body oils, simple repeated extension. The cotton may be perfectly sound at three years while the filament has lost most of its recovery. The garment does not tear. It goes slack at the knee and the seat and never returns, and there is no repair for slackness.

The other loss is visual, and it is the one people notice without quite being able to name. The fades that make old denim worth looking at are the product of a particular yarn, and that yarn is not present in a stretch blend.

Indigo does not penetrate cotton. It sits on the outside of the yarn in thin layers and leaves a white core, which is why denim pales rather than simply thinning. Abrasion at the hip, behind the knee, along the edge of a wallet, removes the dyed surface and exposes white beneath in the exact pattern of one person's movement. Honeycombs, whiskers, the pale crescent where a hand goes in and out of a pocket: these are wear records, and they need a yarn with a dyed shell and a light centre. In a stretch blend the yarn is core spun. The elastane filament is at the middle and the cotton is wound around it. Abrade that yarn and you do not reach a white cotton core, you reach the filament, which is dull and which frays instead of paling. Mills understand this, so stretch denim is generally sold finished, with the fades lasered or printed on at the factory in a pattern identical across every pair in the run and going no further. The cloth is at its most interesting on the day it leaves the shop. Three checks on a rail settle most of it. Find the weight in ounces; a shop that stocks denim seriously will know it, and a brand that declines to print it usually has a reason. Turn back the outseam and look for selvedge, a clean woven band with a coloured line, which means shuttle loom cloth, narrower, more tightly woven and almost always rigid. Then read the composition label, where ninety-eight per cent cotton with two per cent elastane is a different proposition from ninety-eight per cent cotton alone. While the seam is turned back, look at the allowance inside it. A pair with a centimetre and a half to give can be let out twice. A pair with three millimetres cannot be altered at all.