https://ew.com/movies/costume-designers-evolving-female-comic-book-characters-black-widow-loki/
Black Widow costume designer Jany Temime tells EW that a lot of those decisions came straight from Johansson herself. "Because that was her film, and she could choose," Temime says. During one of the initial fittings for the film, she brought Johansson racks of clothes from which to pick Natasha's wardrobe, and she wondered if the actress would choose "something more fashionable, more feminine," but she was surprised at how Johansson went right for the more basic but sturdy pants, shirts, and jackets.
"She picked up a look which was absolutely perfect for somebody who doesn't want people to think that she cares about the way she looks; nothing that screamed fashion, and nothing was planned to make her look sexy," Temime says. "She doesn't need to sell that. She always went for something which was simple and well-made and that she could move beautifully in, not representing a fashion-conscious girl but somebody who is feeling wonderful in her own skin."
That also meant any notion of putting her in high heels was nixed from the very beginning. "Actually, she refused to wear heels," Temime says of Johansson. "Always in the other [films] she was wearing heels on the boots, and she decided this year to not do that. She said, 'This is really uncomfortable and silly. I don't see why, because I'm a female character, I should wear heels. That's ridiculous. It's just an action-y role and I would wear something flat.'" Temime agreed, happy to finally "move on from 'the woman should wear heels' cliche and go into something much more realistic."
Natasha and her long-lost Russian assassin faux-sister, Yelena, spend all of
Black Widow running around in flat-soled combat boots, not a wedge or high heel to be found. And the thoughtful updates were present from the ground up. Temime explains that while Natasha had a special white Black Widow suit made for her as "an American superhero," Yelena simply found her white mission suit on the plane, so it's not form-fitting. But more importantly, it does the job for which she needs it. "She was happy to find the right size, but that was the idea — it's more baggy, the fabric is different," Temime adds. "Her sister's white suit is American, Yelena's white suit is Russian, so it's much more utilitarian-looking. Her sister is a superhero, while Yelena's suit is a military sort of white suit. It's appropriate for missions in the snow. I just wanted to keep it functional."