After a brief break from Instagram last year, Hailee Steinfeld surprised fans with a major beauty reveal: She chopped her hair into a chic bob. The actress, previously known for her long, flowing locks, shared a photo of her new chin-length cut.

Hairstylist Mara Roszak, founder of RŌZ haircare, gave Steinfeld the bob just as she began filming her now-released horror movie Sinners. Roszak recently shared behind-the-scenes details about the transformation, recalling how Steinfeld arrived with nearly waist-length hair. “Hailee has always been a long-haired girl, so this was a big change,” Roszak told Vogue. “I was honored she trusted me with it. We wanted a style that fit the film’s 1930s setting but also suited her everyday life.”

Sinners is a supernatural horror film set in 1930s Mississippi (complete with vampires), with Steinfeld playing an undead Southern woman. Her hairstyle reflected the era’s elegance. “We created an ‘S’ wave shape, which shortens the hair by an inch or two,” Roszak explained. “We left some length to account for that and added subtle face-framing layers, cutting it just above the collarbone.”

Inspiration came from classic Hollywood—specifically Lauren Bacall’s polished, wavy bob in The Big Sleep—as well as sophisticated 1930s women with a “classic and conservative” aesthetic. Roszak dubbed the final look a “swing bob.”

To style Steinfeld’s now-signature bob, Roszak used her own products: RŌZ AIR Thickening Spray for body, ROOT Spray for volume, and Milk Defrizzing and Definition for smoothness. (Beyond Steinfeld’s bob, Roszak has worked with stars like Zoe Saldana and Emma Stone for high-fashion and red-carpet looks.)

Since the chop, Steinfeld has shown off the bob’s versatility—wearing it loose and natural with a side part, sleek and flipped like Gigi Hadid’s go-to style, and now slightly grown out for a more glamorous effect. “Hailee experimented with voluminous blowouts and soft flips at the ends,” Roszak said. “For the film, we styled it in a brushed-out 1930s set.”

Want to recreate Steinfeld’s bob? Roszak’s advice is simple: Ask your stylist for a “long, layered collarbone-grazing bob.”