Like many obsessive collectors, Suzanne Nobles spends countless hours online scouring for treasures. The 25-year-old Arizona-based blogger isn't tracking down rare antiques or priceless baseball cards, though. No, she’s on the lookout for Lululemon.

Racked is no longer publishing. Thank you to everyone who read our work over the years. The archives will remain available here; for new stories, head over to Vox.com, where our staff is covering consumer culture for The Goods by Vox. You can also see what we’re up to by signing up here.

One recent score—a pair of gray and split-pea green running shorts—cost her $95. While they initially retailed for $54, the shorts instantly sold out on Lululemon’s website and in stores, so paying nearly double was Nobles's only shot at adding them to her collection.

"If you want something that is no longer available or that is quite scarce, you hunt it down," says Nobles, who wears her 70-some pieces of Lululemon during CrossFit. "Lululemon makes great technical pieces that fit well, so if I want something, I'm going to pay for it."

When it comes to the Lululemon resale market, Nobles is far from unique. Hundreds of thousands of people are active members of this underground community. There are more than 100 private Facebook groups dedicated to buying and selling both new and used Lululemon items; over on eBay, countless sellers list Lululemon products with 1000 percent markups. Lulu running shorts can go for upwards of $800, as can the brand's vaunted leggings. Bras easily resell for $250, while tanks are listed for $500.

Lululemon is the only label in the athletic apparel space to retain, and even inflate, its value when resold.

Markups like this aren't uncommon in the secondary luxury market, where brands like Chanel and Goyard almost always preserve their high prices, but Lululemon is the only label in the athletic apparel space to retain, and even inflate, its value when resold. Data shared with Racked by online consignment shop Tradesy shows that Lululemon is the fourth most in-demand brand on the site, behind Chanel and Louis Vuitton and ahead of Hermès and Tiffany.

"Lululemon has one of the highest sell-through rates on our site and that data has been consistent," explains Tradesy CEO Tracy DiNunzio. "We’ll sometimes see similar interest with middle-market brands, but this type of demand is unheard of for athleisure. We always see markups in rare Chanel bags or vintage Louis Vuitton, so it’s interesting to see it happening with pants that make your butt look good and only retail for $80."

Lululemon, which would not provide comment for this story, states on its website that it does not support the resale and markup of its items. The company even went so far as to ban suspected resellers last year. However, Lulu fans believe the brand's practices are ultimately responsible for the existence of this fierce secondary market.

While some cite the notable quality of Lululemon products that allow them to hold up well enough to go through several owners, others point to the brand’s strict return policy as an impetus for rabid reselling. Shoppers only have 14 days to return full-priced items, and anything bought off the sale rack is final, inadvertently leaving customers stuck with merchandise they don't want. Why sit on a perfectly good piece you won't wear when you can profit off of it instead?

Then there’s the marketing: Lululemon encourages loyalty by making each item feel special, giving unique names to both items and colorways (yes, there’s a difference between Paris Pink, Blush Quartz, and Pink Shell).

"People who love Lululemon obsessively study and monitor past and current trends."

"People who love Lululemon, myself included, obsessively study and monitor past and current trends," says the Lulu fangirl who blogs at Lululemon Expert and requested I not publish her name. "They treat their clothing like a wearable art collection rather than as garments that will expire or go out of style and need to be thrown away."

"It's for this reason," she continues, "that Lululemon's clothing can both maintain and increase in value over time. Once I saw a Lululemon Define Jacket in Royalty Space Dye sell at auction for $500! These jackets retail for $99. This particular color first appeared in Hong Kong in late July of 2011. How does a jacket fetch over five times its retail value within two years of being released? Simply put, it's Lululemon."

The most glaring cause for this underground market, though, is Lulu's merchandising strategy. Since its founding in 1998, Lululemon has run on a scarcity model: It only releases a certain amount of each style and doesn’t replenish stock once its sold out. Lulu maintains hype among its devoted shoppers by releasing new items every single week, but the scarcity of each piece means enthusiasts lust after sold-out goods.

Plenty of the members of the Lululemon resale community are simply looking to get rid of items they don’t wear; they want to break even by selling these pieces at retail value. Then there are the Lulu superfans that flock to Facebook groups in search of their "unicorn"—that is, a highly desirable item they'll do almost anything to get their hands on. And then you have the Lululemon flippers, usually found on eBay, who hike up the price of unused, in-demand items and make a big profit doing so. One eBay user, who sells under the name ez2curgr8, says she makes her entire living off flipping Lulu.

"Now it’s what I do 24/7—I have over 1,100 listings."

"Initially, I wasn’t planning on reporting it as income, tax-wise, but it became a huge source of profit," says the eBay seller, who's in her fifties and lives in Canada, and requested anonymity. "Now it’s what I do 24/7—I have over 1,100 listings and I sell 50 items a month. The key is patience. I don’t list things right away, so eventually supply will deplete, leading people to shop for my stuff at top dollar."

Another eBay flipper, who asks I call her Marie, says her Lululemon business only provides discretionary income, paying for indulgences like trips abroad.

"My goal is to make back 50—that’s my magic number," she says. "If I pay $50 for an item, I’ll try to get $100. That’s a general markup, but I also research the products to see what they are going for on eBay and try to come close to it. The summer before my husband and I took our trip to Europe, I was making a $70 to $100 profit off every item."

Marie sticks to eBay, since Lululemon Facebook groups generally discourage price gouging. Valerie Higgins, an admin of the Lululemon Exchange Facebook group that has over 22,000 members, tells me that people in her group don’t "make money like on eBay."

"We don't appreciate being used so that others can make money on our efforts," she says. "We created this group so that people can buy and sell without having to worry about paying too much. We can't police everyone, but if we catch someone flipping, we ban them."

Most of Marie’s shopping is done at Lululemon’s outlet store in Orlando; she especially cleans up during their Black Friday sale. Her buying strategy is calculated: Marie uses her phone to search each item’s average resale value on eBay while sitting in a dressing room before she makes her purchases. She’s been able to score pants for as little as $20, and then sell them online for $200.

"We can't police everyone, but if we catch someone flipping, we ban them."

Marie notes that she’s always able to spot fellow flippers—"a random middle-aged woman with her husband, who look like they’ve never done yoga in their life, buying huge piles of product"—and that she's worried about being banned from stores. In fact, employees have refused to sell to her in the past when she’s bought too much merchandise at one time, and eBay took down one of her listings after she used a Lululemon stock photo (all eBay sellers’ photos must be original).

There’s no exact science behind which Lululemon items will become highly coveted, those elusive "unicorns" the superfans obsess about. Experts speculate that functional items like jackets, scuba hoodies, and bags are popular on the secondary market because they're items shoppers are always looking for. Limited edition collections also stoke interest: Pieces from Lululemon's annual SeaWheeze half marathon sell out every year and reliably pop up on eBay with outrageous prices soon after. One pair of shorts from a SeaWheeze marathon collection is currently being auctioned off for $999.

It all comes back to that scarcity model, explains Loree Wasserman, a Chicago-based Lululemon seller who runs the site We Buy Lulu.

"We might start the bidding as low as $10, but a piece will sell for $175 because the print was very sought-after and instantly sold out on the Lulu site," she says. "One season, they made their Wunder Under leggings in a burgundy, and they never sold them in that color again, so we were able to capitalize on that."

Anyone who is a "unicorn thief is taking advantage of the community in a big way."

Wasserman has customers who bid on her Lulu items from all over the world, but Marie says that most of the people who buy from her eBay shop are from small towns in the Midwest who either don't have access to Lululemon stores or perhaps are unaware of how much these items usually retail for. Naturally, some Lulu devotees are less than thrilled with this kind of seemingly dubious behavior. One Lululemon fan who messaged me on Facebook wrote that anyone who is a "unicorn thief is taking advantage of the community in a big way."

The Lululemon Expert blogger also detests "unicorn thieves," but acknowledges that the resale market is enabled by Lulu fans.

"If people on the chat board are going crazy over a particular print or color, you can imagine that it will at least sell out," she says. "And when it does, the lucky few who were able to obtain it may choose to capitalize on their luck and sell the item on eBay, often for a profit. Once those sell out and a few weeks go by, and no new-with-tags incarnations of the sold-out item are showing up on the Lululemon auction pages, you may have a future unicorn on your hands."

eBay flipper ez2curgr8 tells me she knows she is "hated and talked about," but she says there’s more that goes into her business than angry sellers realize: "I'm a business that has to pay 12 percent retail taxes, 13 percent eBay/Paypal fees, 22 to 28 percent income taxes, plus my overhead of supplies and fuel costs."

Not to mention, much of the business is a total gamble. Marie, for example, purchased items from Lululemon’s latest New York City Marathon collection, but the items failed to garner interest on the secondary market. She’s still sitting on them, hoping they’ll eventually be able to be resold; ez2curgr8 is in a similar situation with several winter coats she bought last year.

"If people don’t like my prices, I say, 'Go ahead and invest your own $100,000 in this!'"

"If people don’t like my prices, I say, 'Go ahead and invest your own $100,000 in this!'" she laughs. "If I’m buying a few jackets at $200, that’s $1,000 tied up right there. Every time I buy something, I’m at risk that it might not sell and might not ever be popular."

Last year, Lululemon CEO Laurent Potdevin (who had recently taken over from controversial founder Chip Wilson) hinted in an earnings call that the brand would eventually be moving away from its notorious scarcity model, noting that while the brand doesn’t "mind our guests being hungry for our product, we don't want them to starve for it."

This shift comes as competitors Nike and Under Armour are making it clear they're after Lululemon’s customers. But while the cash from the secondary market is ultimately lining the pockets of resellers—not Lululemon—the scarcity factor is what sets the brand apart and keeps obsessives hanging on.

"A lot of my clients ask if we would buy Stella McCartney workout wear or Athleta, and I just say no," seller Wasserman says. "Why would we take that type of risk when we know Lulu will always have this crazy resale value?"