I have used a flannel tablecloth in the past and hung it on the wall. However, I find it easier and the blocks less of a tendency to fall off the design wall once I started using a large insulator panel covered with flannel. I can lean it against the wall at a slight angle and the blocks stay on better. Lightweight and easy to move if needed. Like Prism99 described.
Jan, I also love your explainations, they add so much to the reply. What occupation are/were you in? Has to be the fabric world somehow! LOL!!