It really depends on what you have available/access to. I work in a warehouse where we deliver a lot of computers so I've taken the foam packing material and layered it together and put back into a pc box. Works great, layered foam has memory qualities so holes seal up pretty much like a Block target. It doesn't stop arrow completely though soIhavebanded some cardboard into a bale and that's the backstop in the back yard. On the course I go to all there target frames are stuffed with old blankets and backed with used carpetwhich stops everything. You couldget a cardboard box the size of your likeingand layer in some carpet backing and carpet. Go to the local carpet store and you probably can talk them out of stuff they've ripped up on jobs or the excess trimmings that are usually left over.Their dumpster is probably full of it. Just a few ideas for you, good luck.