The main benefits of incorporating wood fibers (WF) in plastics are the increased stiffness and lowered cost of the resulting composites. However, these improvements are usually accompanied by a reduction in the ductility and impact resistance. These shortcomings can be removed by effectively foaming and incorporating a fine-celled structure in these composites. The volatiles released from WF during processing are known to deteriorate the cell structure. The maximum processing temperature, which affects the amount of volatiles released by the WF during extrusion of fine-celled plastic/WF composite, affects the cell morphology. This study was undertaken to identify the critical temperature above which the cellular structure of WF composite foams is significantly deteriorated. To clearly identify the effects of the volatiles generated from WF on the cellular morphology, neither a chemical blowing agent nor a physical blowing agent was used in the foam processing. The experimental results show that regardless of the drying method, the highest processing temperature of plastic/WF composites should be minimized, preferably below 170degreesC, to avoid the adverse effects of the volatiles generated from the WF during processing. A method of estimating the emissions from WF during extrusion processing by using the TGA data is also proposed. (C) 2003 Wiley Periodicals, Inc.