Spike Jonze's Her is set in the near future, a world where you can instigate and sustain a relationship with the operating system on your phone, like the protagonist Theodore Twombly (Joaquin Phoenix) does with Samantha (Scarlett Johansson). It's set in a world of computer games and sex lines and porn but at its heart are the things that drive us all: the desire for love and companionship, the desire to be understood and to share a life and experience. And so the fashion in this future world isn't all shiny and space-suity; instead it's low-key and comfortable – the men wear high-waisted flannel trousers; the women colourful separates. We sat down with Her's costume designer Casey Storm to ask him how he arrived at this very particular aesthetic. 

Her is a film about love and sex but while the costumes are very lovely, they’re not really that sexy. Why is that?  
It’s interesting that you say it’s a film about love and sex. It’s definitely a film about love, you know. It’s about love first and foremost. It’s about emotion. The most important thing we were trying to do was portray emotion, portray a soul, not create a cold, distant world. So we wanted to create a palette and a texture and silhouettes that felt comfortable, that people felt comfortable in their own skin. I always think that things that are trying to be sexy are not very sexy. In fact, I think there is something sexy about Joaquin in certain outfits. And I do think there are things that are sexy about Amy [Adams, who plays Theodore's best friend, Amy] at certain times as well. It’s just not your classic idea of the way you would sex things up or be overtly sexy. It’s more about the confidence.

Similarly it’s set in LA of the near future, but it doesn’t feel very ‘LA’. It feels more like Portland, you know, that not exactly hipster thing, but hipster mixed with bookish. Why did you go that way instead of ‘typical LA’?
I wouldn’t say it is or isn’t Los Angeles. I would say again that the most important thing is that we were creating an interesting but not distracting world. It is a bespoke tailored world in the future. You have to access to everything. You can custom-make everything so why wouldn’t you create a place comfortable to you? The clothes that they wear are all indicative of that. We didn’t want to pigeon-hole ourselves by picking a specific style. That would have felt a little too conceptual or contrived.  It was better for us that it be slightly more generic.

"When Spike first wrote it, he had Theodore Roosevelt in his head, and that’s why the character is called Theodore." - Casey Storm

Did you have mood boards or any specific references or how did you arrive at the look?
No, that’s not really how we work. The process of how we arrived at it is that we started our conversations in these big brainstorming sessions. It would be me and KK [Barrett, production designer] and Hoyte [Van Hoytema, director of photography] and Spike and then we would bring in Humberto Leon and we would have these very theoretical conversations about mood and the future and trends without  talking too specifically about buildings or architecture or clothing.

So the first thing that we did was talk about in the future what sort of things would you be doing. Like I was saying before, you'd have access to anything, you could create whatever you want. So we thought if that was the case you wouldn't live in a place that was more isolated and more cold but instead you would live somewhere more warm and more comfortable. Which again led us to think why would we be moving towards future fabrics like metals and plastics and things that often make up a lot of future wardrobe.

Instead we thought well there's a big push now to conserve and be organic and eco-friendly so why not go to that world using cottons and wools and nice textures. Maybe the shapes sometimes are vintage shapes or even futuristic shapes but we're using organic fabrics so that it has a bit of a different feel. So we didn't add epaulettes or badges or things that are signifiers of the future. Instead we took away denim and we took away belts and we took away ties. And that makes a world that's slightly off but feels of our time. 

And there's not really any conspicuous fashion or labels or things like designer handbags that could be recognised. Why did you make that decision?
It's along the same lines, it's distracting. And it doesn't have anything to do with this very small story that we were telling. It's a love story, it's about those two people. They're not people who come from the world of fashion; I mean Rooney's character, Catherine, comes from a slightly more fashion-orientated world and she does wear that kind of stuff and she does have a style that's a little more from fashion magazines, more polished. But Amy and Joaquin, and obviously there's no wardrobe for Samantha, but those characters, they come from a comfortable world where they don't have to show off and they're allowed wear whatever they want. With me, I always like to make average people interesting. Fashion to me is not quite as interesting as ordinary people. 

The blind date character, Olivia Wilde’s character, she’s got a more girlish style. Why is that? 
Yeah, Olivia’s character very much wants to impress him, she wants it to go well, so she dresses up, she’s a little bit more out there. And the character has a little more room to be playful and fun and fashion-y, so then it makes sense for her to wear that kind of stuff.

Why the moustache and the glasses for Theodore?
When Spike first wrote it, he had Theodore Roosevelt in his head, and that’s why the character is called Theodore. And so I think it just hearkens to that era. We kept accidentally referring to that time. So maybe the moustache hearkens to a different era, and certainly the high-waisted pants hearken to that era. And the glasses were something that I wanted to look good on him but I also wanted them to disappear. And Warby Parker make a lot of great frames that do it. There is a tiny part hipster to them but not really, they’re a little bit cool and vintage, but they sort of disappear. And the moustache – I don’t know, I had a moustache at the time, maybe that influenced it. But I don’t know, Spike and I tend to just dress people in whatever we’re wearing. Half the clothes Joaquin wears in the movie are my clothes or Spike’s clothes. The same thing with hair and make-up: we did want to take a direction and stick to a direction and we did want to feel mostly contemporary but also make it feel like it wasn’t necessarily of today so we said ‘let’s have a lot of people with moustaches’ and ‘let’s pick a hair length a little bit longer’. There are very few people with short, shot hair in the film. 

Joaquin’s hair looked really good, I thought, just the colour of it and the way it caught the light.
Yeah it’s interesting, it changes a lot and there are certain scenes where I agree, he looks really attractive and his hair looks great and then there are other scenes where he looks really floppy and sort of like a mess. Generally I think he has something to do with that, it’s the way he plays it. He’s an incredible actor, you know, he messes with his clothes and he messes with his hair and his instincts are always right for what the scene calls for.    

So when you say that some of the clothes were yours or Spike’s, were they just clothes that you own? You didn’t make them? 
It’s a combination, some of them we made, some of them are just literally mine. The red shirt, the shirt of Joaquin’s that kind of became iconic, the shirt on the poster, is just a shirt that I happened to be wearing into the office one day to talk to Spike. And we were both, ‘We should try that shirt on Joaquin and see if he can pull off that bright red colour.' And so we put it on him and I folded the collar inside of it and he looked great and it just worked and we knew he could carry it off without it looking like a cartoon or too poppy even though it was bright red. So we hacked the collar off my shirt and that was the main shirt. 

And where’s that red shirt from?
The red shirt originally is a Band of Outsiders shirt from about five years ago.

Yeah there’s a bit of a Band of Outsiders vibe to the film, isn't there?
Yeah I think so. I like that about it. It’s a little bit bookish, like you said, and there is something slightly LA but a different part of LA and there’s something slightly preppy about it so it covers a lot of points that I wanted to make.

'Her' is released in UK cinemas today, February 14. A clothing collection based on 'Her' is available at Humberto Leon's Opening Ceremony.