I've had 2 pcs of foam insulation covered with offwhite flannel for a design wall for years. I do have to use pins if the a/c is on because it blows the blocks off the board
I have never mounted mine to the wall. I just stand them next to it. I like it that way because I can move them where I want. If I'm working on a big project the stand them next to each other so I can spread things out, but if I'm working on a lap quilt I stack them one in front of the other and just use one.