RE: T-28 Dave Platt
Actually the name of the board is called Celotex. It is also used for insulation on buildings. Try a lumber store other than Lowes or Home Depot. I don't remember how much it cost. The board has lasted a long time. Plus when one side is used up flip it over and use the other side. I think it comes in 1/2" sheets. Its is not very expensive. I'm guessing $15.00 to $20.00 per sheet.