The interior trim pieces on the tailgate are grained, hard plastic. It is completely hollow. There is no insulation there--no foam, no paneling, no gaskets, no nothing. Just welding, molding, and screws.
2001 Audi A6 Allroad 2.7T (C5); 2005 Audi A6 4.2 Quattro (C6); 2005 BMW X5 4.4i (E53); 2008 BMW 535xi Sports Wagon (E61); 2011 BMW X3 xDrive35i (F25); 2009 Audi A4 3.2 Quattro Prestige (B8); 2015 Porsche Macan S (on order)