Costume designer Jany Temime worked on six of the eight Harry Potter, and said she purposefully never altered Snape’s costume.
“I never changed Professor Snape,” Temime told HelloGiggles. “I used the Professor Snape costume and I remade it. I made another cape. I always kept Professor Snape [as he was], because I thought it was a great costume.”
Temime had, in contrast, altered several costume designs from the first two films when she came aboard for The Prisoner of Azkaban. According to Fashionista, since the third film was the first “dark” one of the franchise, she wanted the movie’s costumes to reflect that. She placed a hood and collar on the Hogwarts robes, and gave the Quidditch uniforms a much more rugby feel to them. But when it came to Snape’s outfit, she elaborated, “It was perfect,” Temime said. “When something is perfect you cannot change it. Why should you change it? It was him. And he never changes, Professor Snape. He’s the sort of guy who goes to bed in his costume. Bless him, Alan Rickman.”
Rickman himself made sure the costume fit the character, telling the New York Times he was very involved in the look and that he was “very specific about it. I said the sleeves should be really tight and there should be a lot of buttons.” And the late actor was no stranger to donning all kinds of outfits, from a suited Hans Gruber in Die Hard to a cloaked, Crusades-era Sheriff of Nottingham in Robin Hood: Prince of Thieves. But Rickman said, according to Uproxx, that when he put on Snape’s costume, “something weird took over. It’s the only character and I suppose by my own [insistence] really, never changed his costume over 10 years. Everybody else grew up or had different kinds of outfits. Never Snape and you sort of got the feeling that’s the only thing he’s got hanging in his wardrobe.”