I also made one out of foam insulation board. It was easy to cut to the size I wanted with a steak knife. The insulation board is light violet, if that helps you to go look at it. Then I covered it with the 80/20 batting, as my sister used that on hers and it has worked out well for her.
I am very happy with mine. Oh, wait, I took pictures of it for someone else on the board. Let me see if I can find them. Yup...I found them. Mine slides behind the door to this room.