Until the 1970s, a good many jeans sold had been made of stiff, shrink-to-fit—or "unsanforized"—denim. To soften them, you simply had to wear them. A lot. It took a good six months to properly break in jeans. After a couple of years—years—the hems and pocket edges might start to fray, or a knee would split open. The fabric faded to a powdery blue with some whiskering—the sunburst-like streaks that radiate from the fly. Time and dedication were required to push your jeans to peak fabulousness.

That is, until the popularization of stonewashing in the 1980s. Unsanforized jeans were thrown into industrial washers with pumice stones and tumbled until the denim was sufficiently abraded. (The L.A.-based casualwear company Guess famously had a system that stonewashed jeans for seven hours—a marathon now considered an environmental horror.) Sometimes jeans were further distressed with acid, sandpaper, rasps and files to mimic the previously hard-won wear and tear. The entire operation was christened "finishing" and conducted in "washhouses," sprawling facilities that now process thousands of jeans a day.

A largely agrarian economy only 15 years earlier, by 2018, there were roughly 6,000 textile and garment production companies in Vietnam, employing 2.5 million workers, and accounting for about 16 percent of the country's exports and more than $30 billion in revenue. Experts believe that last figure will jump to $50 billion by 2020.