Found insulation

I finally made a decision on my insulation. A big batch of four-inch thick Polyisocyanurate showed up on craigslist for a price I couldn't refuse. I sacrificed a bit of my desire to have more natural materials in my house for a product with an incredible R value, light weight, ease and stability. Polyiso insulation is a rigid foam board with an R-value of about 9 per inch, making my roof R-36. It is easy to use since the sheets can be cut to fit the stud pockets with just about anything with a slightly cerated edge. It will not settle over time which is important for my roof since it will be moved around from time to time and it will add some rigidity to the panel. Best of all, I only paid $12 per 4'x8' sheet. I am happy with my decision, even if I will never be able to pronounce the chemical name of the stuff.