Thanks for all the responses.

I was wondering how that 1/2" building insulation might work or even the green fan fold. I currently have a Block 24" x 24" x 18" target. I think it ran me about $100. I shoot both broadheads and target tips into it. I like it pretty well. I think the key to any target is the thickness from front to back, because the real damage starts as soon as you start blowing out the back of the target. I have tried everything from feed sacks filled with rags to hay bales. I once concocted a haybale press which I made out of 2 - 4x4's with all thread between them. As the hay loosened up I just tighted the nuts on the all thread compressing them tighter. It worked well but I didn't have a roof over it so the hay deteriorated pretty badly by the end of the season. My main thought behind making one of these was to be able to make something larger to mount between a couple 4x4's planted in the ground with a roof overtop where a couple or three guys could shoot at the same time. If your going to buy a layered target I wouldn't recommend anything less that 18" thick with the speed and energy of todays bows you will be blowing out the back of it in a couple rounds of shooting.