I use a regular white shower curtain and it works great. You will lose a little brightness but with the modern projectors it's not much of a problem. There are other materials but I found a lot of them would hot spot in the center. A shower curtain is so cheap that if you don't like it you can move on to something else. The picture quality is just a clear as a monitor, the projector determines that, 1024x728 and up is very clear.
I've attached a pic but unfortunately the camera and the dark room makes it seem blurry but this is at 1024 x 768 and full scale. The great thing about a projector is you can adjust the size of the image to suit the simulator scale. Hope this helps
