For Your Consideration: Dylan O'Brien's Blond Buzz Cut

Because Vanis was working with color-treated hair on set, the biggest goal was to keep it looking healthy throughout filming — "especially because Zoey had the blond in the front and we sometimes had five [hairstyle] changes in a day," she says. "I was obsessed with the Ouai Heat Protecting Spray ($28). Any time we had to flat iron her hair, I used that."

Then, she relied on the May11 Hair Oil ($83), and the team "went through bottles" of the In Common Hair Elixir ($32), which is meant to strengthen the hair and add shine. "We used a lot of products to coat her hair to make sure it stayed really healthy," Vanis says.