Sienna Miller tries on a new role

Miller expects to catch some flack as an actress entering the fashion world, but she said the feedback had been kind for the most part. “If I was on my own, people might just think it was a quick fix, but because Savanah’s a designer, it sort of makes sense. I know what I like, and I can describe it, but she’s the genius.”  (Luis Sinco / Los Angeles Times)

The private trunk show at Neiman Marcus in Beverly Hills launched the collection in Los Angeles.  (Luis Sinco / Los Angeles Times)

The Twenty8Twelve collection debuted in stores this month.  (Luis Sinco / Los Angeles Times)

Miller said the idea for Twenty8Twelve came about when Spanish entrepreneur Carlos Ortega approached her with an offer to design her own line. She was, at the time, the spokeswoman for Pepe Jeans, one of Ortega’s many companies. “I think he wanted to do something that was young and was a smaller, boutique-y brand,” she said. “And we don’t want [the brand] to be this enormous global thing. We want it to be quite small.”  (Luis Sinco / Los Angeles Times)

Miller, left, and her sister Savanah, who is a graduate of London’s Central St. Martins College of Art & Design. Savanah said her sister’s untrained eye would be integral to the label’s success. “She comes up with crazy ideas that I never would because your [formal design] training limits you,” she said — like jeans that zip up the back. “The factory will say, ‘No, we can’t do that.’ But they do, and of course they’re fantastic. She’s good at pushing things a little further.”  (Luis Sinco / Los Angeles Times)

From the Twenty8Twelve collection: Peony cashmere-silk top ($230) and Pearl slick-wool pants ($300).  (Luis Sinco / Los Angeles Times)

Aubrey cashmere-silk top ($260) and Camille jeans ($210).  (Luis Sinco / Los Angeles Times)

Capulet prison-stripe dress ($460) and Timmy slick-wool jacket ($430).  (Luis Sinco / Los Angeles Times)

Ophelia habutai silk blouse ($380).  (Luis Sinco / Los Angeles Times)