Don't try to lie to us: you saw Quentin Tarantino's Once Upon A Time In Hollywood and you thought – maybe once, maybe more than once – that you should invest in a Hawaiian shirt. And moccasins. Maybe a leather jacket and all. It's an achingly stylish film.

So when we met Arianne Phillips, Tarantino's costume designer on Once Upon A Time, in the wood-panelled back room at Musso & Frank on Hollywood Boulevard, we couldn't not quiz her on how she made everyone on screen look so damn good. The legendary lunch spot has had pretty much every film industry notable of the last century stop by at some point: Chaplin, Monroe, Garbo, Warner brothers Jack and Harry, Bogart, Pitt, Clooney. A couple of pals called Rick Dalton and Cliff Booth dropped by there for a meeting with an agent, too.

Standing in front of a line-up of costumes worn by Leo DiCaprio as Dalton, Brad Pitt as Booth and Margot Robbie as Sharon Tate, she talked us through all the details you'll never be able to see on film, working out what each character's talisman is, and finding the perfect yellow Hawaiian shirt.

preview for Once Upon a Time in Hollywood trailer (Sony)

What details are there in the costumes that you and the cast would know about, but which a viewer might not be able to see?

The details are always really important to me. They help create layers in the character, they also, I hope, assist the actors in becoming that character. So for instance, this medallion which I had made – on this side, there's an R for Rick, and this side is kind of a Tudor rose pattern – was inspired by the idea of that kind of Steve McQueen bad-boy kind of thing. This belt also has an initial – you know, the person that has monogrammed clothes has a bit of an ego, a bit of bravado. So I love that for Rick.

For Cliff, we have this stuntman's buckle. Sometimes when I'm working on a film incredible magic will happen where I'll find a piece of costume that is directly, I think, like a shaman or a talisman for that character. So I was rummaging at Warner Brothers costume, which is a giant costume house, and I came across this belt buckle which says 'Stuntman's Association Member'. I think they were [from] 1965 onwards. So these belt buckles were something that if you were a stuntman, you could get you could have made for you, and this became like a eureka moment for me for Cliff. I was so excited. And luckily, Brad Pitt and Quentin were both really enthusiastic as well, and he wore this belt buckle with all his costumes.

Once Upon A Time In Hollywood
Sony Pictures

And then for Sharon Tate, for Margot Robbie, we had the great good fortune of having Deborah Tate, Sharon Tate's sister, as a consultant. And Deborah was generous enough to show me Sharon's clothes, some of her jewellery, her sunglasses. Just to be able to touch and feel those, there's an osmosis. I think that, you know, there's a reverence and a responsibility that I felt as a costume designer in recreating who Sharon Tate was. And luckily to be able to have anecdotes and stories from her sister about who she was was really, really important for me.

I asked Deborah if there was any way that we could possibly borrow a couple pieces to use in the film. It was unremarkable – it wasn't particularly like, amazing jewellery. It was just a few bits and bobs that had been leftover from years of, you know, holding on to Sharon's stuff. And Deborah was generous enough to loan it to us. So basically the whole film, [Robbie's] wearing a ring or an earring that belong to the real Sharon Tate.

How did you settle on Cliff's Hawaiian shirt?

So, in Quentin's script, it was scripted that Cliff Booth wears a Hawaiian shirt. Hawaiian shirts are kind of part of the Quentin Tarantino vernacular. We've seen them before in other iterations of his films. So I knew that this needed to be unique to once upon a time in Hollywood. And of course, Quentin and Brad wanted to be unique. So for me, I looked at every vintage Hawaiian shirt you can imagine. And in the end, I was inspired to make this shirt which is based on similar vintage shirt that I had seen, but we changed the pattern to be not a Hawaiian motif, but an Asian motif with the Hawaiian shirt cut, just to keep it in its own world. And yellow: I used a lot of yellow in this film. For me, yellow really represents California, it's a colour that was very commonly used in the Sixties. And it looked particularly good on Brad Pitt.

Once Upon A Time In Hollywood
Andrew Cooper//Sony Pictures


And what about the shoes? Rick's cowboy boots and Cliff's moccasins are kind of the distillation of the two men.

Rick wears cowboy boots even when he's not working. And he wears them because they're cool – I think if you imagine the feeling of wearing cowboy boots, it makes you feel kind of like a badass, right? Tough, strong, protected. It's a pair of boots he probably would have worn on Bounty Law or Lancer, so it's part of his persona. [For] Cliff Booth, on the other hand, we were quite inspired by the Tom Laughlin movie Billy Jack, which is this kind of denim-on-denim thing. And the idea of him wearing moccasins was just badass in a different way. It's total confidence, right? To wear a soft shoe like that.

You think about the scene with him and Bruce Lee, knowing how confident he was. So I felt like there's a dangerousness in wearing moccasins. He doesn't have to prove to anyone he's a tough guy – he's a stuntman, he throws himself off buildings. And so I love the vulnerability and the strength it would take for a person to wear moccasins. And also, it's a little hint that Cliff is aware of what's going on [culturally] – moccasins are something that the hippies and young people were wearing. And it also goes to his silhouette of being casual of being very comfortable in his clothes. So that's the thinking behind that.

Once Upon A Time In Hollywood
Andrew Cooper//Sony Pictures

How do you choose what colours you're going to use?

In my opinion this is probably Quentin's most reportage film – it's not as highly stylised as other films that we know him to do. Inglourious Basterds, that also felt reportage in a way. So, [I started by] looking at Bob Richardson – the cinematographer who has a long working relationship with Quentin, and he's so brilliant and a master – and how he photographs, and in my opinion what colours really looked beautiful. And Barbara Ling's production design, and what the colours were of the time and what works good on film. I don't use a lot of green usually as a costume designer because I find it doesn't calibrate well to DVD. Red, even, I don't use very often – I did use red here [on Rick's dressing gown], which was unique, but we loved the traditional Chinese red silk colour. But I find there are certain colours I usually stay away from. I think browns and oranges and yellows are really indicative of the period.

Once Upon a Time... in Hollywood is out on digital download on 7 December and 4K Ultra HD, Blu-ray and DVD on 9th December