FREEPORT — Like shrinking Arctic sea ice, sales of jackets at L.L. Bean are an indicator of warming winters.

Ten years ago, the best-selling jacket at Maine’s flagship outdoors retailer was a heavily insulated parka rated for temperatures between 10 degrees and minus 40. Today, the top seller is an ultralight down jacket rated between 25 and minus 25.

Coming on strong is a down sweater that weighs almost nothing and is rated between 30 and minus 20.

A warming climate might be hotly contested by some, but the appeal of a lighter winter jacket isn’t. It’s an industry-wide trend driven by consumer demand, not science or ideology.

“It has been the biggest shift in the outerwear business in the past five years,” said A.J. Curran, product director for outerwear at L.L. Bean. “We call it seasonal versatility. People can use (these jackets) through a normal winter day, what has become the new normal.”

Behind the new normal in outerwear is a string of warmer-than-average weather readings.

Globally, the top 10 hottest years on record have occurred since 1998, according to federal weather-tracking agencies.

In the United States, last winter was the warmest since record-keeping began in the late 19th century. New England was warmest of all the regions, with Maine 8.6 degrees above average. Yes, everyone was bundled up during the polar vortex in 2014, but clothing makers don’t design for one extreme year. Overall, they’re shifting to season-straddling winter wear that’s comfortable over a wider range of temperatures.

The trend is well documented in specialty publications.

Women’s Wear Daily previewed this fall’s line of men’s outerwear by Woolrich, calling them “transitional pieces that can be worn at different temperatures.” Those include field jackets in stretch material for easy layering, Gore-Tex jackets with thin padding and – a first for Woolrich – an Arctic parka without fur.

Outside magazine interviewed analysts and manufacturers who were reporting a shift from heavily insulated jackets to mid- and lightweight. A 7-ounce down jacket is the top seller now at Mountain Hardwear, while a similar garment is topping sales at Eddie Bauer. The magazine noted how textile makers Polartec and PrimaLoft now offer thinner “active insulation” to replace down and bulkier synthetic fill.

That synthetic insulation, called PrimaLoft Gold, is inside Bean’s $139 Packaway jacket. It’s designed to provide comfort at 35 degrees with light activity, ranging as low as minus 15 degrees with moderate motion.

THE APPEAL OF MORE VERSATILE CLOTHING

Susie Jiles of Boothbay has one. She was wearing it last week, standing at a special display of Downtek water-repellent goose-down jackets that greets customers as they walk through the Bean store entrance next to the giant boot.

Jiles was looking at an Ultralight 850 down jacket. It’s rated at 25 and minus 25 degrees and sells for $199. She was comparing it to a $189 Ultralight 850 down sweater, which is rated at 30 and minus 20 degrees. Weighing just 10 ounces, the sweater can be stuffed into its side pocket, shrinking to the size of a grapefruit.

“I might wear this right through the winter,” she said.

That’s what Fran Walker plans to do.

Walker was visiting from Greenville, South Carolina, and wanted to replace a heavier ski jacket. Greenville is in the foothills of the Blue Ridge Mountains, and winter nights can go below freezing. But daytime temperatures can rebound above 50 degrees, so Walker said she wants something more versatile. Besides, she said, Greenville doesn’t seem as cold as it used to be. She remembers skating on a local pond in college, decades ago.

Walker tried on and bought a black Ultralight down sweater.

This is a common buying trend in parts of the country with moderate winters, Curran said. He was in New York City two weeks ago, and it seemed as if half the people on the street were clad in light down.

“Lighter-weight jackets are becoming the uniform,” he said.

STEADY DEMAND FOR LIGHTER WEAR

Bean sales reflect the transition. Ten years ago, the biggest seller was the Rugged Ridge Parka, which features a waterproof nylon shell and a generous filling of synthetic insulation. Rated at 10 degrees and minus 40, the $189 coat is still for sale. But you have to walk through a multicolored forest of down jackets at the main store here, or scroll down into the Bean website, to find one.

The same is true of the $249 Baxter State Parka, the warmest coat Bean sells. Packed with goose down and featuring a faux-fur hood ruff and waterproof shell, it’s rated at 5 degrees and minus 45. Field-tested in extreme winter conditions in New Hampshire’s White Mountains, the ad copy brags.

Sales jumped for the Rugged Ridge and Baxter State Parka two years ago during the polar vortex, Curran said. But the demand for lightweight jackets didn’t slow, he said, evidence of a true market shift.

The extreme up and down of the past couple of winters has made it tricky for retailers to know which jackets to carry, according to John Reny, president of the Maine-based R.H. Reny department store chain. His buyers have to make plans soon to order outerwear for the winter of 2017-18.

At Renys, the best-seller for men is a Carhartt cotton duck work jacket. It’s heavy and flannel-lined. But clothing technology – such as higher fill power for down, which traps more insulating air pockets – means a jacket can weigh less and still be warm. And special features, like the reflective lining in Columbia’s Kaleidaslope II, claim to reduce heat loss. It’s the most-popular jacket for women at Renys.

But if a warming world has grown-ups lightening up, the trend has been slower to take hold for kids’ jackets, Reny said. Maybe it’s because parents can’t help but worry about their children being cold.

“They squish a jacket, to see if it’s thick enough,” Reny said.