An extruded composite adapted for use as a building material includes a core having a base polymer and a natural fiber in a substantially homogeneous mixture and an ionomer capstock. To improve adherence of the ionomer to a base polymer, the ionomer can be mixed with a similar or substantially similar base polymer prior to coextrusion with the core. Additionally, various additives may be mixed with the capstock material to improve visual aesthetics of the product and performance of the building material, especially over time.