NEW YORK — For Mary-Kate and Ashley Olsen, it's all about speaking softly and sewing a mean seam. When the twin sisters, 24, launched their upscale clothing line The Row in 2007, they wanted to be as incognito as possible.

"It was something where we didn't want our names on it. I even went as far as being, 'OK, who can be the frontman?' We can make the clothes and someone else can be the frontman," Ashley says, sipping coffee in the brand's downtown office. "Instead, it was more about letting the product speak for itself and us being quiet. It's five years in, and we've stuck to that model." 

On Sunday, the intensely private and press-shy designers are going a little more public with their spring/summer 2011 collection. They're showing it in Paris and airing footage from the show on Bing.com.

"It's the first time we've allowed people behind the scenes, which I'm excited about. It's another way to become a bit more personal," Mary-Kate says. "We're all growing up. The brand, my sister and I, the customers, the retailers — it's nice to be able to allow them to see the brand grow in a more accessible way."

And they hope to expand into handbags. "We definitely look at this brand as a lifestyle luxury brand," Mary-Kate says. 

Adds Ashley: "It's a small company. You need to take baby steps."

In person, the sisters are diminutive but formidable. They passionately discuss every seam, pleat and piece of fabric in their line, which is sold at Bergdorf Goodman and worn by Lauren Hutton and Charlize Theron. Mary-Kate is more boho, in a loose-fitting blue sweater from The Row, worn as a dress and paired with gladiator stilettos. Ashley is more classic, wearing black palazzo pants, a blouse and jacket. They proudly show a visitor the signature tailored jackets and flowy frocks hanging on racks in their conference room.

"We wanted it to be a little more feminine and a little more lady in a way, but wanted to do constructed, so it's a little more modern," Mary-Kate says. "We wanted to offer the great suiting we've always had, and the tailoring. With the soft dresses, there's a lot of form-fitting and sexy ..." 

Ashley interjects: "It's also taking the heart of The Row and where it started, and then elevating it and really working with the silhouettes." 

Both are perfectionists, they admit. "It takes 2½ days to do one jacket. It's all handmade," Ashley says. "Those are the things we love doing. It's the attention to detail."

And yes, they work daily on their brands: the JCPenney line Olsenboye, the midlevel Elizabeth & James collection and The Row.

"Yesterday, we were here from 10 (a.m.) until 11 (p.m.)," Mary-Kate says. "We sign every check. We're in every meeting. It really comes down to Ashley and me."

They finish each other's sentences and complete each other's thoughts. And mid-interview, Ashley wipes an invisible bit of dust off Mary-Kate's nose.

Their one point of contention? Who has the bigger closet.

Says Ashley: "It's about the same."

Mary-Kate: "Mine's a bit spread out. You definitely have more shoes than I do."

Ashley demurs: " I don't think so at all."