I use white felt stretched over the pink insulation boards from hardware store. The felt holds blocks up beautifully, and when you have a larger piece with lots of seams which make it heavier, a straight pin into the insulation does the trick. I too vacuum. Did not wash, but certainly could have -- poly felt is washable. I went with felt because I was able to get a 96 inch width so no seams in the wall. And it was a lot cheaper than equal amount of good quality flannel would have been.