Styrofoam, ethafoam, a green beef hide stretched over raw meat. Arthur, I may be misunderstanding this. In his momentum test the KE was the same for the two different arrows. He had a light arrow and a heavy arrow then shot them throgh a chrony at different speeds until they both had the same KE, which I belive was 50. His conclusion at identical KE the heavier arrow, which would have more momentum, did not outpenetrate the lighter arrow.