“The thing that really caught my attention was the fact that it was about sisters,” Este Haim explains.

The Grammy-nominated artist is speaking of the new Netflix romantic comedy, Voicemails for Isabelle, which leans heavily into the bond of sisters. If anyone knows about sisterhood, it’s surely Haim, who’s spent her entire professional career singing to hoards of fans alongside her own sister.

Haim and Amanda Yamate co-scored the film, set to drop on Netflix Friday (June 19). The collaborators join The Hollywood Reporter on a video call to discuss the Leah McKendrick-directed film, their latest project with the streamer.

“When we all watched it with Leah for the first time, we pretty much all just turned to each other and agreed this requires a love theme,” Yamate says of the film’s most vital relationship, which is not the one viewers might expect.

In Voicemails For Isabelle, Zoey Deutch plays Jill, who starts recounting her life adventures to her beloved sister that recently passed. Jill’s relationship with Wes, played by Nick Robinson, is the romantic driver of the film, but her relationship with Isabelle, her sister, is the real centerpiece. The composers picked up on that quickly.

“The main theme is a love theme for Jill and Izzy, the sisters. Wes and Jill don’t even really have a love theme,” Yamate says. The track, “This Party Sucks Without You,” which THR is exclusively revealing, is repeated throughout the film. They add, “It’s in there five or six times.”

Yamate and Haim jumped into the film quite early, as far as timing for composers goes. They built that main theme off the logline alone. “We like jumping in early because you just get to know each other as creatives for a little bit longer,” Yamate says. They point out, however, that McKendrick had been working on the film for eight years.

“We’re really big to experimenting as much as we possibly can on prescore, just to even see what’s rattling around in our heads,” says Haim. The musician says the pair treat it like a “musical word dump” in a way.

The pair found moments for experimentation through some of Wes’ moments. “[He’s] this hot Texas boy, so he had his own Texas sound,” Yamate explains.

For “This Party Sucks Without You,” however, Haim and Yamate decided to try some live winds and live string, which is when things started clicking. “Those moments between Jill and Izzy are so raw and delicate that I feel like [that’s] the instrumentation Leah was liking,” says Yamate.

The score process for Voicemails For Isabelle was mainly typical for the partners, with a slight difference. “The process was actually that we just cried,” Yamate jokes. Their collaborator agrees. “Oh my god, every day,” Haim adds.

“This score was just special for us because we got to sing on it,” Yamate says. The pair had never sung together before. Adds Yamate, “It just made so much sense.”

For Haim, the film was a bit more personal than most projects. It was a major factor in taking the project for the musician. “It was a rom-com, but it was really about family and loving having such a deep connection to your sister,” she says. “Clearly that’s a huge component of my life.”

Haim also felt another connection with the film, particularly with Izzy, who was ill for much of their lives. “I’m a type one diabetic and have Hashimoto’s and neuropathy, and a whole laundry list of ailments that can sometimes hinder me from living my best life,” she explains. The musician notes that her sisters and bandmates, Danielle and Alana, are there to witness on a daily basis.

“It’s definitely grating on me, but it’s also not lost on me that it can be really exhausting for them too. But they never let me see that. They never make me feel like I’m too much or I’m a burden or anything that I need is too much,” Haim says.

She adds, “When you have chronic illness, you never want to be a burden on people. I really felt the first during the [beginning] of Voicemails that I was connecting with [the sister’s] dynamic.”

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Voicemails For Isabelle premieres June 19 on Netflix.