"I think our shorthand that we have with each other makes it easier," says Fey. "Neither of us has a sister, we both have brothers." "I'm personally a little obsessed with sisters," chimes in Poehler. "They are exotic creatures to me. I love being around them and watching them interact. It's like a special language. I think that Tina and I are chosen sisters, so I think it's been fun to experience that thing I never got to experience in real life. We have a moment in the film where we first see each other and just pick on each other like apes. We find that physicalness can be really sisterly - very specific to that relationship."

Sisters Tina Fey & Amy PoehlerSisters Tina Fey & Amy Poehler

In addition to the sister thing, both actresses enjoyed playing with their public personas. "There's a moment," says Poehler, "where Tina's character Kate decides for once 'I'm going to be responsible for tonight' and my character Maura decides 'I'm going to really let loose'. So it's like everybody's wish fulfilment in the film. Everybody gets to be the person they didn't get to be."

"I think it's fun to be able to play a character that's in no way aspirational and in no way a role model," laughs Fey. "The more female characters there are on-screen, there's less pressure on every character to represent everyone. I love playing people who are flawed!" And after their experience in television on Saturday Night Live, 30 Rock and Parks and Recreation, both loved being able to play to an adult movie audience. "Immediately the impulse is to curse so much," says Fey. "Then you realise you're cursing more than any actual person would and you dial it back."

"I think we're doing some fun stuff here that we've never gotten to do before," adds Poehler. "A lot of physical, active stuff, which we're excited about too. I don't know if we think about it while we're doing it, but it's fun to not have to think about it." "Especially because we've both done TV," Fey continues. "I like the boundaries of network TV. I think you have to work a little harder when you can't just show a boob."

Watch the trailer for Sisters here: