I've started using acrylic felt from the craft store for all my wall hangings - two layers if I want some "puff" to my quilting. It's washable, cheap, and holds up well. You can purchase it by the yard. I even sometimes use it as the "frame" around my wall hanging by appliqueing my front to the felt, leaving an edge around the center. You can't iron on top of the felt, however, since it could melt.