Plastic, and the detail is quite fine - I actually could have paid more for finer detail, but for $32 I got all of this (minus six steps I already removed):
It seems like a real game-changer, for parts not popular enough to be produced in brass. Browsing through the site will blow your mind. A word of advice: I tried to paint a few of these with enamel paint, and the paint is still wet 6 weeks later! Acrylic works much better.