Unfilled polygons in ArcMap are filled in an exported KML.
Symbolize a polygon layer in ArcMap with a border only, and a null fill color. Export with the Layer to KML tool. Add the KMZ back into ArcMap and the polygon has a white fill.
The KML file has the tag
Documentation states that "The layer symbology will be used as the KML symbol." but this is clearly not the case.
Bug or feature?