Made it out of Homasote sound barrier board and covered it in wine-colored fabric. Could use some trim on the outer edges to make it look cleaner, but im not rushing to do that. Not only is it easy on the dart tips, it also deadens the overall sound of the darts hitting the dartboard.
Half inch thick. Cuts by scoring a couple few times with a utility knife. After installing, I had to move my line 9/16" away from the dartboard.
I laid out the fabric and got it tight with wood working clamps. Cut my board to size, sprayed the board with spray adhesive and laid it gently on the fabric. Then i folded and cut the excess fabric around and stapled down the back.
Im sure there’s a cheaper material than Homasote that would work, but my board hangs on a door that goes into the living room, so the sound barrier was a nice bonus for me.