My design wall is a piece of flannel thumb tacked to the wall. Works fine unless the window is open, then the pieces fly. I also have a small block board, a piece of 2'×2' sanded plywood from Home Depot covered with Warm & Natural batting. I love the block board, that has saved me so much ripping time.
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You can see both the design wall & block board in this picture, plus the area is tidy for a change:-)