I got mine from the company I work for, we mainly specialize in industrial fabric products. The material was called vin-a-sign or something like that. It's the same stuff that they make vinyl banners from. It's durable and has a matte finish on it, which is what you want for photography. The only problem is that we only have it in 5' rolls, so to get something wider, they had to weld pieces together, leaving you with a seam. With good lighting and a bit of touch up in photoshop, it hasn't been a problem though.
I see that you can order them in larger widths (seamless) but those get to be really expensive.
Also, I have found that while it's more durable than paper, it's not so easy to clean. Also, I've had to roll and fold mine up many times, so it has small wrinkles. Again, good lighting can make them practically invisible to the camera, but it's still not that perfect surface like when it was new (and when you roll out new paper).
If I shots in a studio on a regular basis, I'd probably go with paper because it looks great when you first unroll it.