The best way I can describe it is PVC rectangles on a lycra backing. Definitely not a satin but due to the spaces in the PVC it isn't as "thick" as a solid PVC could be.
www.spandexhouse.com had one with less of the back showing in their stretch hologram (page 6) but I didn't originally use it because of the hologram effect. However, since I ended up spray painting it anyway, I could have.