ULine sells a foam board at this size relatively cheap. I used a lot (many, many) comic boards for short yardages and the heavy ULine ones for the long yardages. Love the way it turned out. Learned of the "library book shelf" storage system on this web site. Love it, Love it. Took a while to wrap all my stash though!

fabric boards
 

Yes, you can look around and find fabric boards cheap. I go to sign shops and get the ends off of plastic sign boards. Buy them for a few pennies and come home and cut my own with a utility knife. The sign companies love this as they make money and get rid of them at the same time. For the larger flate folds I leave the sign boards longer and it works out really great. Hope this helps everyone.

Amazon has the comic backing boards. 100 for about $12 right now.

Thanks so much, just ordered 3.......