I went to JoAnns and got a load of their cardboard things they wrap fabric on. I cut each one 23" to fit the height of my shelf and wrap fabric on each one. You can get more boards on the shelf than if you use the cardboard things as is. I had read an idea somewhere else that said use foam board, but the foam board is $2.89 each (and you get 7 pieces from each one) and the cardboards are free. So far, they seem to be holding up.