They’re trendy. They’re ugly. And they’re year-round business in Boston.

While most in the city are focused on catching rays in the warmer months, Boston’s vintage clothiers spend the year hunting down the best ugly holiday sweaters to meet demand, they told Metro.

“We keep a back stock of Christmas sweaters so when it comes time for it we have plenty to choose from,” said Lisa De Freitas, manager for the Buffalo Exchange store in Somerville.

The store’s collection comes from drop-ins who sell their old clothes, trading them for cash or store credit. By the time the market for supplying ugly sweater parties picked up again this year, she said, the store had amassed ten boxes worth of tacky Christmas-y finds, from the horrendous to the adorable.

De Freitas’ favorite this year featured a “Santa Christmas cat” with a mustache made out of gemstones. It sold for $18.50, she said.

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And they sell out almost as soon as they hit the shelves.

“People really get a kick out of outdoing each other,” she said. “It seems to get bigger every year."

Vintage clothes and holiday sweaters have become a profitable side gig for Brian Mack, of Southie.

On treks around New England, he said, he picks up the best ones at consignment shops and thrift stores. He sells them on Craigslist for between $20 and $50 a pop. He’s sold 150 so far and still has 50 more.

“You have to drive way far away,” he said. “Not in the city. Everyone looks for them in the city.”

Mack posted a few dozen fliers around the city and said he wears the best of his crop during his shifts working at Boston nightclubs, where he hands out business cards when people marvel at their old school charm.

“Advertising,” he said.

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The ugly sweater game has become a big part of Marlene Clauss’ job as owner of Great Eastern Trading Co., the Cambridge vintage mainstay.

The sweaters at her store are handpicked for ugliness, and sometimes un-ironic quality, said Clauss (pronounced like “Santa”). Most fetch around $20 but can run as high as $55 on the high end.

It takes a shrewd eye to find the winners.

“Within the Christmas sweater world the best ones are jewels,” she said. “Flying pigs and ice-skaters, those are the ones everyone wants. There’s a lot of dreck out there that no one wants.”

And it’s now become competitive, Clauss said. She told Metro she has ugly sweater suppliers both in the Boston area and near L.A., but wouldn’t name names.

“I would have to kill you if I told you,” she said.