Fashion brands have been falling all over themselves to snatch a piece of thegrowing market for stylish athleticwear (aka athleisure), but it's not as easy as just throwing a few leggings into a line and hoping people wear them to SoulCycle. A new collaboration between Derek Lam and Athleta, launching Wednesday, should be an example to fashion brands looking to get athleisure right.

Nancy Green, Athleta's president, met Lam after being introduced by Khajak Keledjian, the founder of Intermix. (Both Intermix and Athleta are owned by Gap, Inc.) "I wanted to do a collaboration with somebody who's a really important designer, who would understand and really get this category and this woman," Green says. "Derek understands the modern woman who lives her life on the go and he's very interested in this category." Both sides had much to learn, though, before this capsule collection — which includes both lifestyle pieces and true activewear — came together.

Leather joggers and shorts were initially a shock to Athleta's design team. "We'd only worked in leather once," Green recalls. "[We thought], it's a really cool idea, but how are we going to make that work?" Green says that it was especially difficult to fit the leather pants, but the team managed to do it without the dreaded bunchy "pooch" in front. (Readers, I bought them. At $398, they're more expensive than anything else Athleta carries, but compared to this $695 pair from Vince, they're a bargain.) Similarly, a parka had to be reimagined in nylon because the team could not get the fit and proportions with the original fabric right. The cashmere sweaters are a perfect example of the combined vision — a gorgeous oversized, fashion-y drape with a flattering, butt-covering fit.

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Lam has struggled to introduce true performance-wear into his own 10 Crosby Derek Lam line. "Before this, we'd added pieces, but I was really never satisfied because we could never get the technology to be something you could use [for working out]," Lam says. "I've looked at other people who are ready-to-wear designers doing athletic clothing and sometimes I feel like it looks like it but it doesn't really work like it." He cites challenges sewing technical fabrics and constructing pieces, like bras, seamlessly.

Besides the leather pieces, the elongated, color-blocked bra tops are Lam's favorite items in the collection. "That was technically so challenging for the factory, but they solved it," Lam says. The matching performance leggings were also carefully designed so that the seams curve in such a way that they're extremely flattering on the body. (I bought the blue color-blocked cropped version, too. They have the best waistband I've encountered in workout pants in awhile.)

So what will both brands get out of this three-season collaboration? It's hard to say. For Lam, he says he's willing to design at lower price points "if it’s bringing something fresh and new" to the marketplace. "I'm not so into fast fashion, but if there's an intriguing story behind it, then I go for it." He says that this type of clothing is the new sportswear, and he clearly gained some valuable insight into the technical production process. For Athleta, success will be defined by a multitude of factors, such as how many new customers the aspirational collaboration nets the brand. Green was noncommittal about her plans for future designer collaborations, saying that this first one was a learning experience.

However, it seems that the collection is already resonating with customers. While it launches broadly online and in select larger stores on Wednesday, Green says the company is already seeing promising early sales from its online preview session. "This line will bring new customers into the brand and it will also very much appeal to a customer who really loves fashion and who knows about Derek."

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