AbstractWhen increasing the wood fiber (WF) content in extruded wood fiber/plastic composites (WPC) foams, a good balance between reducing the cost and obtaining good cell morphology should be maintained. This study examines the relationship between WF content and the foam morphology in WPC foams. The role of WF as cell nucleating agent at low concentrations (10 wt.%) was observed, as WPC foam with 10 wt.% WF had lower average cell size and higher cell density than neat HDPE foams. Increasing the WF content further, decreased the average cell size and cell density, and increased the foam density of WPC foams. These results were linked to the rheological properties and crystallization behavior of HDPE and WPC with different WF content.