I tried a bag of cellulose insulation packed down and all of the rounds save a 380 penetrated the bottom but not by much as they were on the ground in front of a barrel I had stood up to catch the lead. I tried another barrel using the top I had cut off with several layers of tin in front of it then the insulation and the 9mm rounds went right through it so I'm abandoning the idea. I think I will try some of the rubber mulch and see how that works. I hope my wife dosn't go out back in the next few days and look at the tree edgings before I get to the Lowes this weekend.