Sienna Miller and designer David Neville at Rag & Bone's new Soho, NYC store. Photo: Rob Loud, Getty Images

Rag & Bone
designers Marcus Wainwright and David Neville celebrated the opening of their new Mercer Street shop in Soho, NYC last night with a pretty unassuming party... except for, well, Sienna Miller, who was making the rounds, drinking champagne and playing with Neville's toddler son, Dashel (mom is makeup artist Gucci Westman).

"We've known Sienna since she was 15-years-old," fellow Brit Wainwright told StyleList.

"We weren't designing back then, but we were just living in London and knew her socially. It's pretty surreal that she's done so amazingly well. We dress a lot of cool people, and she's definitely one of them."

For the store opening, the duo dressed the pint-sized starlet in a boyish get-up of grey chambray mini-shorts, a hunter gray blazer, scarf and Rag & Bone's black "Newberry" booties.

But it's models, not actresses, who seem to be inspiring Wainwright and Neville these days, with mannequin Jessica Stam collaborating on their current Spring 2010 designs, and Maryna Linchuk previously playing a similar role.

"Models get exposed to more clothes than anyone else, aside from magazine editors," explained Wainwright of the fascination.

"And consequently, I think it's very important to look at what they are wearing. A lot of them have really awesome style and they wear it so well."

As for the new vast Soho digs, which feature Rag & Bone's signature worn-in, rustic feel, Wainwright says it's a totally different vibe from their boutiques in the more neighborhood-y West Village neighborhood of Manhattan.

"It's a quiet block, so it's not crazy Soho, but we thought we'd try this out and see what the tourists think of Rag & Bone," he explained, adding that they are thrilled to be neighbors with their friend Phillip Lim, whose shop is next door.

"We know Phillip pretty well because we were in the CFDA/Vogue Fashion Fund together," he said. "We have dinner quite regularly."

And perhaps now regular coffees across the street at Cafe Duke. Tourists: get your camera phones ready.