Cut 3/8" foam core art board to any size you like. Cover the foam core art board with one or two layers of light Dacron batting used for quilting. Use spray craft adhesive to hold the Dacron in position on the front of the foam core, and use duct tape to fasten the Dacron on the back side of the foam core. Cover that with an outer fabric of your choice, again using duct tape to fastening the outer fabric to the back of the foam core.
Mount to the wall using heavy duty Velcro.
I have six of these in my living room. Most people think they're just decorative panels.
My 30"x30" panels costs about $15/ea, with the largest variable in the price being the cost of the outer fabric.
