Technically speaking, the Orbit batter bass drumhead is comprised of a 10 mil clear Dynaflex film for the top-ply. For the under-ply, Attack uses a 10 mil nebulous white Dynaflex film with calculated sized and placed orbs. For our resonant ported bass drumhead, we replace the under-ply head with the 10 mil black Dynaflex film. Attack chose to include the Holz branded 4” porthole to protect and give that perfectly finished appearance.