Why did Eric and Dylan wear dusters?

Trenchcoats I can understand. I go to a university with a lot of international students and I see a handful of people everyday wearing trenchcoats or something adjacent to them everyday, especially during the winter. Dylan and Eric's ""trenchcoats"" are really just dusters, which ive never seen worn by people in everyday life except maybe for costumes.

Did the TCM wear cowboy-style leather dusters like Eric and Dylan did, or were they actual trenchcoats?