I have used cardboard of any description cut into 2′ x 3′ pieces. After they are cut, they need to be glued together. It takes about 12 – 15 plies depending on the thickness of the cardboard. Regular white wood glue works good. I usually water it down slightly so it goes further. Pour the glue with a small amount of water in a pail mix it thoroughly. Apply it with a paint brush between each layer. Once everything is glued The backstop needs to be compressed somehow until the glue has cured. Laid on top of a table with lots of weight on top works good. After it has cured, the edges can be trimmed on a table saw and duct tape applied to edges.
Need to work fairly quick during gluing process!
Boxes that vinyl siding come in work great.
Only cost is the glue:wink:
Bruce
