This looks like a ballistic rubber they recycle and use on police ranges. It absorbs thousands of rounds before even showing a hole, but it can't be that product because it says "DIY" so I'm at a loss. Would like to see printed details instead of watching someone shoot at it.
“Malo periculosam, libertatem quam quietam servitutem." (I prefer the tumult of liberty to the quiet of servitude.). Thomas Jefferson
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke, Loosely translated from Thoughts on the Cause of Present Discontents. (1770)