Diane Widas is the costume designer on Supernatural.
Diane featured in the "Meet the Crew" chapter in the Supernatural: The Official Companion Season 1, where she said:
The two challenges of a show like this are you have to make regular people look interesting...these boys live out the back of their car, so they got well-used looking items of clothing, so it's not just off the rack a lot of times. You might get your heart set on something specific, but we might need eight or ten of them because they are major action heroes. And Jared is a very tall boy, so I end up making a lot of his coats because they're really hard to find in eights or tens. For Jensen, he has the journal, so we build a pocket in all of his coats so that he has a place to put that.
Diane was also in charge of the costuming for Divine: The Series.
- Diane Widas on IMDB