“It’s been said that making a collection is like having a child,” said Kate Mulleavy, who co-founded the fashion label Rodarte with her sister Laura in 2005. They were calling from Rodarte’s California studio just weeks before showing their debut couture collection in Paris. “But now, I think making a film is really like having a child.”

Last week at the Venice Film Festival, the duo finally gave birth to their first feature-length film, Woodshock, which they’ve spent the past five years writing and directing together. Starring their longtime friend, Kirsten Dunst as Theresa—a woman who helps her ailing mother die using poisoned medical marijuana from the dispensary where she works—the film invites viewers to get lost with her in the maze of California’s redwood forests, which act as a metaphor for the depths of Theresa’s grieving subconscious. (The film is out in the U.S. on September 22.)

Laura, 36, and Kate Mulleavy, 38, were raised to love cinema; their mother once encouraged them to take a week off of school to watch all of Alfred Hitchcock's films. And while Woodshock is their first feature—inviting comparisons to fashion’s leading designer-turned-director, Tom Ford — they’d already dipped their toes in seven years prior when they did costumes for Darren Aronofsky’s Black Swan.

Kate and Laura Mulleavy, who grew up with the forests of Santa Cruz as their backyard, said their childhood in the trees had a profound impact on how they looked at the world. “If we had to entertain ourselves, we’d just go be imaginative in this natural setting," Laura said. "Later, when we were approaching writing the film, we knew that we wanted to somehow try to portray the magnitude of these trees and the feeling that they can cause to a human.”

The name Woodshock refers to the psychological condition that people experience when they're lost in the woods, begin to panic, lose touch with reality, and, in some cases, perish. For Theresa, nature offers an alternate reality, but one that is just as haunted as it is cathartic. She spends her days working at a weed dispensary with an endearing grouch named Kieth (Pilou Asbæk), while her boyfriend, Nick (Joe Cole) makes ends meet at a lumber yard. Images of daisies blowing in the wind are spliced with shots of saw blades singing through freshly cut tree limbs; crushed berries wiped across lips lead to blood spilt.

“We used the idea of the destruction as a subliminal threat,” said Kate. “It’s not only about violence between humans, but also the violence that happens against the environment, but that we’re almost unaware of in our daily lives.”

Natural motifs are often woven into Rodarte’s collections, as evidenced by the brand’s first couture show, which took place this summer in the gardens of Paris’s Cloître Port Royal and featured baby’s-breath tucked into models’ hair. But the difference between designing for fashion week versus a movie is that costumes serve a certain character’s mental state. As Theresa goes deeper and deeper into the woods, for example, the slip dresses she wears, which belonged to her late mother, fall apart and become more ethereal, too. For another plot point, she wears a shimmering black dress inspired by a black widow spider’s exoskeleton.

Instead, the parallel between fashion and film reveals itself in Woodshock’s rich tactility, whether it's Theresa running a bloody finger over a lace tablecloth, or visual techniques such as double exposure and reflection to create a sense of layering.

“For a sensitive person like Theresa, the visual and textural parts of her relationship to the things around her is very much in line with exploring what her subjective experience is,” said Kate.

“Our goal was to break down the film layers into frequencies,” Laura added. “Sound, touch, image, dialogue—all those things come together and create the narrative of the film.”

To help them achieve all the above, they recruited Christie Wittenborn to help with the film's costumes; Peter Raeburn for the music, and Peter Flickenberg was given the weighted task of cinematography for a film with very little dialogue and a loose plot. Oh, and they prefer not to give it a genre, either.

As with everything the Rodarte sisters do though, they produced Woodshock together, from start to finish. And although they’'ll continue to show ready-to-wear twice a year, they are committed to filmmaking in the future as well.

“This was the most inspired I’ve felt as a creative person,” said Laura. “And I think it’s made me a lot more confident as a designer.”

Watch: Kirsten Dunst Opens Up About the Movies That Make Her Cry