A process for in-line extrusion of polymeric coatings onto roofing shingles during manufacturing includes moving a web of shingle substrate material in a downstream direction and extruding a liquefied coating of polymeric material onto at least one surface of the moving web to form a thin film. The liquefied coating may be a molten polymeric material that forms a thin film on a back surface of the shingle material to prevent sticking and eliminate the need for a traditional back dusting with material such as powdered stone. The polymeric film further may be applied to the substrate material in lieu of a saturation coating of asphalt, thus reducing cost and weight while providing a comparable moisture barrier and a lighter more flexible shingle.