A process for producing plastic/wood fiber composite foamed structures includes the steps of pre-drying wood fiber filler; mixing it with plastic to form a mixture; feeding the mixture into an extruder; introducing and mixing a blowing agent; subject the mixture to high shear forces and extruding the mixture to produce a plastic/wood fiber composite foamed structure. The filler has a degradation temperature and an active volatization temperature. During the pre-drying step the temperature is maintained below the degradation temperature. During the mixing step the mixing temperature is maintained below the active volatilizing temperature. During the introducing and mixing step a blowing agent is introduced into the plastic/wood fiber mixture and is mixed therewith to produce a plastic/wood fiber/gas mixture. During the subjecting step the plastic/wood fiber/gas mixture is subjected to high shear forces in the presence of high pressures and the temperature is maintained below an active volatilizing temperature.