Dave Daines, 34, recently ditched his brown leather briefcase for a backpack. The account planner, who spends a quarter of his time on the road, said the switch was motivated by "sheer functionality."

"I got tired of having this man-purse, messenger-bag-style briefcase strewn over my shoulder while I'm going through customs with my luggage," said Mr. Daines, who now has a Herschel brand backpack for everyday use and an expandable Incase model for when he travels. "That backpack is my portable workspace and overnight bag."

Mr. Daines is just one of a growing number of executives choosing to stick with the backpacks they carried in college over the briefcase that was once considered the badge of professionalism. Key among the reasons for the backpack's growing popularity among professionals: Versatile new styles that make it an appealing accessory in a hands-free digital age.

In the U.S., backpack sales for adults over the age of 18 were up 33% for the 12-month period ending in May 2014 compared with the same period a year earlier, according to consumer-tracking data by researcher NPD Group. Sales among women rose 48% to $311 million, while men's sales grew 23% to $385 million.

With so much technology out there, professionals want speedy access to all the items they carry with them. Rather than tossing their cellphones, tablets and laptops haphazardly in a briefcase, they're turning to backpacks. "With the digital age, we have become attached to so many things that we need bags to be functional," said Durand Guion, men's fashion director for Macy's. "The need to have our hands free has propelled the backpack into the forefront."

Brands like Tumi, a high-end luggage manufacturer, have taken note and adapted their product lines to better fit consumer needs. Tumi's business collection that features numerous styles of professional backpacks -- the brand's fastest-growing business style category since 2010.

"Customers want their bags to do more for them," said Alan Krantzler, Tumi's chief merchandising officer. "A backpack is more versatile. You can stick a laptop in there or even your gym clothes if you wanted."

Tumi's spring 2014 campaign, called "Global Citizens," prominently features composer Eric Whitacre wearing a backpack in a testament to the growing emphasis the brand is placing on the accessory. Ad agency Yard worked on the push, which featured a catalog, online video, social media, e-commerce and an international media buy.

The introduction of hip, versatile styles have also helped elevate the backpack's perception. Herschel, founded in 2009, creates high-quality backpacks in a variety of sizes and styles, allowing people to accessorize, look professional, and carry everything they need with them.

"We started out on young professionals' backs," said Mikey Scott, global marketing director for Herschel. "People are drawn to products that are utilitarian and modernized, but still look classic."

Other brands, like Eastpak and JanSport, have also introduced lines designed for the workplace. They include cord-organizer pockets, laptop sleeves and areas for miscellaneous items. Many of the styles are casual, but clean. "The backpacks that are out there now aren't embarrassing to bring into a boardroom or business situation," said backpack-wearer Mr. Daines. "I don't see carrying a backpack as less formal than a messenger bag or briefcase."

But don't put the nail in the briefcase coffin just yet. Not every job is conducive to backpack-wearers. "A backpack would make me look like a joke," said Richard Myrlak, a 26-year-old realtor who carries a briefcase.

Briefcases are still the go-to accessory for professionals like Mr. Myrlak who want to make an impression in business meetings, presentations or special events with a briefcase. But even those have evolved from the classic attaché box-style case with slimmed down designs that are softer, more casual, and feature more pockets for various electronics.

The executive is "carrying that throughout the day and into the night and weekend," said Kevin Korney, senior division merchandise manager for Fossil Lifestyle, where "work cases" are still the top sellers. "It's about making sure it fits into his lifestyle, not just the corporate culture."