I've used cotton batting; it worked well for me, but I just don't really have much wall space. Then, I moved to a Cheryl's (I think that's the name, it's a portable design wall that collapses). It's okay, but units and blocks often fell off. Now, I have 2 panels of the foam insulation board that I covered with an inexpensive flannel sheet from Amazon. It's been the best solution yet for me. I can kind of lean them against the wall, then move when not needed.