Plastic rivet.

To fit:
Boxster (986) 1997-2004 - Used in the front bumper assembly, underbody linings and wheel arch liners
Boxster (987) 2005-2012 - Used in the scuttle panel cowling
Cayman (987C) 2006-2012 - Used in the scuttle panel cowling
911 (996) 1998-2005 - Used in the front bumper assembly, underbody linings and wheel arch liners
911 (997) - Used in the scuttle panel cowling and cabriolet top frame