The fabric feels like a silky nylon perhaps.
There is a small hole and a worn area on the front as shown in the photos. The zipper has some corrosion. Please inspect all photos carefully for details. The fabric has a vintage dye odour.
I am not sure what it's original indended use was. Could be a grad gown, judicial robe, graduation regalia , a choir robe or something else. Could be worn as a magician teacher costume.