THERE'S not a hint of rivalry between 'best friends' and sisters Hilary and Haylie Duff who are living it up on the set of their new film Material Girls.

Few things capture the public imagination so much as the hint of sibling rivalry - particularly when it concerns famous sisters. Just ask Dannii and Kylie, or Ashlee and Jessica.

It's an accusation that's dogged Hilary Duff in recent years, particularly since her older - and less well-known - sister Haylie has carved out a career of her own roles in films such as Napoleon Dynamite. Yet Duff junior is having none of it.

"It's almost insulting to me when people are like, 'Aren't you guys jealous of each other? Don't you get competitive?'," she said of the rumours.

"She's my blood - we're a little team. There's no animosity or jealousy or anything like that.

"We've always supported each other and been happy for one other and we push each other to do things that challenge us. If I get some great job offer she's just as excited for me as if had it been given to her and vice versa."

Indeed the teen queen is quick to point out that if it were not for her big sister, the global empire that is Hilary Duff may never have been.

"When I was younger I didn't really know I wanted to be an actress or a singer," she said.

"My sister wanted to do it and so I wanted to do it because I wanted to be just like her."

Now the Duffs have teamed up on screen in the school-holiday friendly Material Girls, in which they play pampered heiresses who fall on hard times.

"My sister's my best friend so just to get to go to work with her every day and share a trailer with her was really exciting," Duff said.

"We did a movie together when we were younger where we played sisters, but we were just extras in it and we were like, 'Some day we'll get to be the main characters and play sisters again'."

With her 19th birthday looming later this month, Duff said she was at a crossroads between her tween-icon origins and the promise of an edgier, more sophisticated persona in the future.

"At the time when I did all those movies (Cheaper By The Dozen, A Cinderella Story) that was what was being offered to me and they happened to all be the nice girl who was going through some kind of dilemma," Duff said.

"I was so young at the time and I didn't want to play some pregnant, cracked out, drug-addicted teenager.

"But now I think it's nice that I can move on and do things that are different."

But Duff has no plans to turn her back on young fans in the rush to reinvention.

"It's really important to me to know that I have a younger fan base to pay attention to. I feel so lucky to have a clothing line and stuff they can always feel a part of," she said.

"I don't want to grow up too fast, I don't think I'm in any rush. It seems like everyone turns 18 and they want to prove that they're not a child anymore - and then when you're 26, where do you have to go?"

It's a refreshingly grounded outlook that's helped Duff escape the accusations of bratty behaviour that have bruised the reputation of peers such as Lindsay Lohan.

"I have a job that's very out there and crazy and fun and it's easy to get caught up in and to believe in your own excitement," she said.

"It's easy to start to believe how great you are, but really it's just a job. My mum and my sister - we're so close and we talk about things that are real.

"I don't have that many friends but I have a handful of close friends who know everything about me and will tellme if they think I shouldn't be doing or saying something."