In the past few years, scientific and industrial research has been increasingly focused on the study of composite materials comprising wood fibers in thermoplastic matrices. Plastic/wood-fiber composite products are currently used in the building industry for siding, window and door frames, and decks as a replacement for conventional pressure-treated wood lumbers.These products are resistant to moisture and insects and do not rot, split, warp, and splinter compared to traditional treated wood lumbers. However, plastic/wood-fiber composites do not come without trade-offs. They are more brittle and have lower impact resistance than neat plastic products. In addition, the density of plastic/woodfiber composites is almost twice that of solid lumber. These drawbacks may prevent plastic/ wood-fiber composites from achieving their full potential in the conventional structural lumber market. Substantial research efforts have been made to address the drawbacks of plastic/wood-fiber composites. Recently, the concept of creating cellular foamed structures in the composites through batch or continuous extrusion processes has been successfully demonstrated to significantly improve the shortcomings of these composites.Because of the presence of bubbles, the density of plastic/wood-fiber composites has been greatly reduced, and significant improvementsintheductilityandimpactresistanceof the composites have also been achieved. However, most studies on the extrusion foaming of plastic/wood-fiber composites with chemical foaming agents (CFAs) have centered on the investigation of styrenics, polypropylene, and poly(vinyl chloride) asmatrices.Thereiscurrentlyalimitedamount of information available on the extrusion foaming of polyethylene (PE)/wood-flour composites, although PE represents the largest portion of the wood–plastic compositesmarket,accountingforalmost70%ofplastics used in the manufacture of wood–plastic composites. Consequently, it is of great importance to study the foamability of PE/wood-fiber composites through an extrusion process, and this was the goal of this study