Americans bought more backpacks than ever last year— 174 million of them, according to the Travel Goods Association. The bulk of these were purchased during back-to-school shopping season, typically the second-largest sales season for retailers and an important bellwether for year-end holiday sales.

But there is ample hand-wringing within the industry that it is not keeping up with the times. After growing at a fast clip over the last decade, as offices grew more casual and men increasingly switched from briefcases to backpacks, the market for backpack sales in the United States is expected to grow just 3.9 percent this year, according to data from Euromonitor International. That is down from 9 percent five years ago.

“The market for backpacks is becoming saturated and is nearing its peak," Ayako Homma, a Euromonitor research analyst, wrote in an email. Consumers, she said, are “looking for something new and different.”

Those concerns add to pessimism over the entire late-summer shopping season. Consumers will spend about 6 percent less on back-to-school purchases compared with a year ago, the National Retail Federation predicts, in part because there are few new “must have” electronics so far this year.

In backpacks, too, experts say there is a dearth of hits. They say innovation has stalled in a market dominated by VF, which also owns the Eastpak, Timberland and North Face brands and controls 55 percent of backpack sales in the United States. Many packs on students’ backs as they go back to school this week are largely indistinguishable from those their parents carried.

“I think there’s room in the market for something new,” said Lindsey Shirley, a clothing and textiles expert at Utah State University who is developing a new degree in outdoor product design to address a perceived shortfall of fresh talent in the field. “There’s definitely room for innovation.”