I took 4 of those 1/4" foam boards (sold by the poster board) I duct taped together on both sides so they would stay in one big piece. I covered it flannel from Joanns. Works like a charm. The foam boards were $2.49 a piece, flannel was on sale for like $2.25 (50% off) I think I used a yard and a half. I already had the duct tape......so it was a very inexpensive project.