What should an animated elephant, anthropomorphized as a shy teenage girl with a crush on an ice-cream vendor, wear onstage while she performs Aretha Franklin’s “I Say a Little Prayer” in front of said vendor?

This was the kind of question facing Laura and Kate Mulleavy, better known for designing the fashion brand Rodarte, three years ago, when the sisters were brought on as costume designers for the animated movie “Sing 2” by the company Illumination, best known for bringing “Minions” into the world.

It wasn’t the sisters’ first time designing costumes for a feature film about performers working thorough their issues onstage. In 2010, they cocreated costumes for Darren Aronofsky’s ballet gothic “Black Swan.” But it was their first time designing for an animated cast of zoo animals, which included a pig (voiced by Reese Witherspoon), porcupine (Scarlett Johansson) and lion (Bono) putting on a space opera in a Las Vegas-type town.

There were more questions, of course — questions that came up for the entirety of production, Kate Mulleavy said: “How do we get the movement right? How do we get the texture right? How do we get this as detailed as possible?”

Here, in an interview condensed and edited for clarity, the sisters discuss the complexities of fashion animation, including their inspiration for the film’s standout costume (worn by Meena, that lovestruck teenage elephant): a crystal-encrusted hooded cape in several shades of blue that cloaks a long white gown with a giant train — all ruffles and chiffon and unabashed innocence.

How do you even start designing something like that gown for animation?

Kate Mulleavy: There’s so much heart and soul in her character, and we wanted to reveal that in her costume change. When she takes off the cape and reveals this beautiful dress, the train kind of floats, and it’s actually so spectacular to watch. Trying to get that thing that chiffon does when you have a magic gust of wind … animating that was just a very long process.

Laura Mulleavy: Her cape, if I’m correct, took a year. There were things on it that we really wanted to achieve, like hand-smocking detail. It’s so easy in animation to make something perfect. And what we wanted to bring is the fact that what we do is either handmade or a hand-done technique — something that makes it look special and interesting, not like a cookie-cutter item.

Even down to the shape of this smocking and the crystal application and then the dégradé within the cape. It took such a long time because it wasn’t just like, “Oh, let’s make dark blue and teal come together.” We had to recreate an effect that you would get from hand-dyeing.

Those details, going back and forth and making sure that the blue was swishing across her in the right part — that took a lot of work.

You released a few Rodarte collections in this time period, between 2018 and 2021. Did any aspects of your work on “Sing 2” seep into those collections, or vice versa?

Kate: Sometimes this question comes up when you costume-design — if you’re coming, in our case, from your own fashion company. How much should Rodarte show up in the costumes? We definitely have a viewpoint, creatively, and those things can become intertwined in a sense.

Rather than having the movie influence what we were doing, it made us rethink things that we’ve done. Sometimes you compartmentalize. You do something and you never think about it again. With fashion, you’re always trying to move forward or take new steps in a different direction, even if it’s within your language; the handwork that we’ve done over the years — aging, beading, hand-dyeing and a lot of techniques that we said at the time we’re never going to do that again.

This was, in a sense, a pretty straightforward costume design project. But in fashion there has been a lot of attention lately on the “metaverse,” and brands translating their looks for avatars in video games or animated characters. For you, did working on “Sing 2” feel connected to that phenomenon at all?

Laura: I don’t connect them. It’s definitely in the zeitgeist, but this is a feature film that took three years to do. It doesn’t seem like a gimmick, and that’s not what it is. Fashion going into those spaces is a way to make money, and I don’t think that’s bad. I think that’s great, it’s what we do. It’s exciting, and it’s a way to create brand awareness.

Kate: But our main idea was to take some of the handmade things we’ve done and see them in a new space. So in a sense, there is something meta about it because there is a reference to things that we’ve done. I feel like if you loved Rodarte, you could watch the stage show at the end of the movie and see that.

Laura: I think it all goes back to virtual reality. “Sing,” yes, puts me in a space closer to understanding, like, what is the virtual reality version of what we do? That is definitely the future.

Kate: I walked away and I thought, “All this time I’ve made all these clothes that exist as objects.” We have a whole archive of what we’ve done. And here’s something I’ve made where there isn’t any physical object, and I feel like it’s as real as anything I’ve ever made and could be something that someone looks at 100 years from now. It’s creatively exciting to know that you can go beyond what is material.

“Sing 2” will be released Dec. 22.