I got the 48" square, and it's awesome. We don't have hay bales, so we put the face on bundles of trash cardboard. It works perfectly.
As the other reviewer said, the target is a plasticized paper. It says "waterproof" on the corner, and I believe it. Of course the arrows make holes in the paper (it is a target, after all) so it will eventually wear out, but that will take 100s of shots. It's not like a pistol target, where you need a fresh target to know which holes are yours. When you go to collect your arrows you can tell which ring you hit, even if the target is absolutely full of holes.
One note: The bale of hay shown in the picture would only be sufficient for youth bows. An arrow from a modern compound bow would go clear through, possibly damaging the fletchings or resulting in loss of the arrow. We put a wood backstop behind the compressed boxes because even they are not sufficient for our Genesis bows. The hope is that the boxes slow the arrows down enough that they aren't damaged by contact with the wood.
Safe and fun shooting.