Like a lot of successful entrepreneurial ventures, Chrome Industries was born of out dissatisfaction. Its founders were a group of Boulder, Colorado, cyclists who couldn't find a messenger bag that met their standards—so they started making their own, using military-grade materials and salvaged seatbelt buckles. Now based in San Francisco, Chrome has been selling those messenger bags for almost 20 years, alongside a growing collection of similarly tough backpacks, apparel and other gear.

The latest addition to that collection is a line of what Chrome calls "knurled welded waterproof rolltops," released two weeks ago. The four bike bags (two backpacks, a front-rack duffle, and a saddle bag) sport roll-top closures and distinctive exterior seams with a nubby texture—evidence of that "knurled welded" technique, which the company says creates superior durability with very little weight.

Left: one of the two backpacks in Chrome's new line of roll-top bags. Right: a close-up look at the knurled welding

Chrome's head of product, Ben McCosh, explains the advantages in more detail: "The difference [between] our knurled welded technology and a traditional lap weld is in the seam/bond strength," he says. "The knurled weld embosses the fabric and welds it together to create a mechanical interlock at the same time as a welded seam. The embossing or 'mechanical interlock' creates 50 percent more surface area than a lap weld where the seams holds together." That translates to seams that are, McCosh says, 1.5 stronger than you would get with a traditional lap weld.

These external welds also make the bags watertight, eliminating the need for the waterproof Cordura liner that Chrome adds to its other bags; that reduction in material makes for especially lightweight bags. (They range in weight from half a pound for the front-rack duffle to 1.7 pounds for the larger backpack.)

But finding a factory to execute the knurled welding wasn't easy. "Factories make money by making the same thing they made yesterday," says Chrome's president, Steve McCallion. "We had to convince the factory that there was an opportunity to do things differently." And once Chrome found a willing partner, there were numerous rounds of testing and prototyping to wrangle a wide range of variables—everything from the right proportion for the knurling texture to the proper amount of cooling time in sequencing the production.

Above: early thumbnail sketches from Chrome's design team. Below: a more developed drawing of one of the new roll-top bags

Knurled welding isn't the only innovation Chrome developed for the new roll-top bags. For the front-rack duffle and the saddle-bag versions, the company also wanted to create "a hardware-free bike bag solution," McCallion says—meaning no annoying clips or hooks weighing the bags down. Instead, the company devised a rack adapter that works with loops on the bags, allowing the hardware to stay on the bike rather than travel with the bag.

McCallion is confident that the end results stand up to Chrome's promise of making "bombproof" gear. "People write us letters about how they're out on a trip biking, had an accident, and landed on their Chrome bags and it saved their lives," McCallion says. " We take those letters seriously. All our bags are guaranteed for life. When you make a promise like that, you better be doing it right."