Please be careful using the cardboard from fabric bolts. It is not always acid free. I've been seeing some fabrics (LQS and others) that show ghosting where you can tell what area was around the board edges. Ghosting is when you see lines on the fabric and it always shows up more the closer to the cardboard core of the bolt. You never know exactly how long fabric has been on a bolt in a warehouse in all sorts of conditions and reusing those cardboards for your loved fabrics isn't the best idea. I'd hate to hear of someone's favorite fabric decaying because they inadvertently kept it on one of these cardboard pieces.