I've been hearing from a lot of people who are excited about using recycled billboard fabric as a cheap/free material. One guy is making a yurt with it, another is using it as roofing and a pond liner. While I like the sound of free, I wonder about the toxicity of the stuff. I think most of it is PVC. I'd especially love to hear from anybody with background in chemistry who could explain what kind of off gassing or degredation to expect.