This invention provides improved lightweight reinforced roll-up door panels (20) The improvement includes: the panel being formed of an extruded plastic material, such as EX75 Resin ABS, and having upper and lower longitudinal edges (25, 31); the panel having an outer skin (22) and an inner skin (22) spaced from said outer skin; at least one pocket (24) positioned between the skins; and an insert (28) positioned within the pocket. The insert is so configured and arranged as to resist flexural deformation of said panel.