For 11 months during the year, they sit neglected and unwanted in closets and on the shelves of secondhand stores.

But come December, those tacky holiday sweaters — featuring garish reindeer, snowmen, Santa and Christmas trees — are all the rage. There are websites, such as uglysweaters.com, and books, such as “Ugly Christmas Sweater Party Book: The Definitive Guide to Getting Your Ugly On,” dedicated to the phenomenon.

“We can’t hardly keep a sweater,” said Dave Blackburn, store manager at the Salvation Army Thrift Shop, 1601 W. 23rd St.

Blackburn thumbs through the now sparse men’s sweater section that’s been picked through heavily the last few weeks. He said that on a given weeknight, dozens of college students comb the racks, looking for the perfect sweater for any assortment of holiday sweater parties.

“Parties seem to be really big this year,” he said.

The demand for tacky Christmas sweaters has increased the past six or seven years, said Corey Sievers, store manager at Arizona Trading Co., 736 Mass.

And it’s growing.

“I’ve burned through more this year than I have ever before,” said Sievers, who stocks up on the sweaters year-round. He estimates that about 200 sweaters have come in and out of his store this season.

It’s pretty slim pickings at his store as well. Sievers shows off what’s left: a snowman mock turtle neck and a couple of generic, but nonetheless tacky, sweaters.

But even the bottom of the barrel will get snatched up, Sievers predicted.

“We always sell every last, single one,” he said.

Sievers’ advice for getting that perfectly ugly sweater? Start early.

“Keep your eyes open all year,” he said. “If you see a good one, nab it.”