"We want things that are going to be flattering for a variety of shapes," Fleiss said. "We want lots of different styles. At the end of every buying season we'll get together and evaluate if we have the right amount of pink dresses vs. gray dresses, the right amount of long vs. short."
Another factor in what Rent the Runway adds to its collection: What fans on the company's Facebook page say about New York Fashion Week.
"We encourage our users through Facebook to vote on different styles," Fleiss said. "People will say love it, OK or don't like it and we'll factor that into our buying decision. It's a good way to immediately gauge interest on a type of style."
When it comes to black-tie fare, Rent the Runway often looks to the red carpet and buys the same designs the stars wear.
"Many of our dresses actually are worn on the red carpet," Fleiss said. "It's not, 'Get the look that's similar,' it's 'Here's what the stars actually wore.'"
Among the celeb-certified designs carried by Rent the Runway are dresses worn by Kim Kardashian, Taylor Swift, Claire Danes and Gwyneth Paltrow. A sequined Badgley Mischka dress currently available on the site mirrors the one Carrie Underwood wore to last month's Golden Globes. The jade green hue Angelina Jolie rocked at the Globes pops up on many Rent the Runway dresses too.
In the coming year, Rent the Runway plans to add more designers to its ranks, explore the plus-size market and look into international expansion. Though it peddles in temporary glamour, the company wants a permanent place in women's closets.
"We find that many times a woman's first experience is during prom, then we get her for college formals and for weddings she's attending and then maybe for baby showers or black tie events," Fleiss said. "There are so many special events in a woman's life and so many reasons to dress up for them."