Credit: Photograph by Talia Herman

To its ardent fans, selvage denim is more than a fabric. Like Detroit techno or classic cars, it's a sub-genre with a fanatical following of would-be connoisseurs. The furor is all the more impressive given that what makes it special is purely technical: selvage simply refers to denim woven on a shuttle loom, a piece of equipment common in America before modern jet looms proliferated in the sixties.

"What that essentially means is that the denim took longer to produce; it was run at a slower pace and there are little imperfections in the fabric," explains Kiya Babzani.

Unlike modern looms, which create 90-inch-wide swathes of fabric, shuttle loom strips are generally between 29 and 32 inches wide. The edge – or selvage – of denim strips created on a shuttle loom are visible along the seams of so-called selvage jeans. Flip a pair at the cuff and you'll see a narrow white band of fabric punctuated by a red stitched line flanking the main leg seam. That's the selvage, which is traditionally red but can be whatever color a brand selects.

As selvage denim made on shuttle looms has regained popular over the last decade, the term has become synonymous with premium jeans. Because of that, many people assume that selvage is better quality than denim produced on modern looms. Don't be fooled.

"Maybe 10 years ago it was an indicator that it was a better built product, but now it's not at all," says Babzani.

When it comes to quality, experts peg Japanese-made selvage denim as the world's best thanks in large part to Japanese factories' high production standards. But plenty of non-Japanese brands also produce selvage. Today, you'll find it on the shelves at Nordstrom, J. Crew, and even Urban Outfitters. The only way to really assess what you're buying and how it will fare over time is to look at jeans that have been worn a while. "It's important to find photographs of what the jean would look like after a year of wear, after two years of wear, that's really what determines how good the fabric is," says Babzani, who recommends visiting the Super Denim message boards on superfuture, where denim nerds compare pics. It's an extra step, but it is the only way to make sure you're investing in a pair of pants built for the long haul.