Wood plastic composites were prepared through impregnation of solid wood with polyethylene. The effects of impregnation parameters on polymer retention and hardness were investigated. A screening strategy of 16-run resolution IV design for seven factors at two levels was adopted. The seven factors were: ratio of maleated polyethylene in formulations, ratio of polyethylenes with different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). Polymer retention (PR) and Brinell hardness (H-B) were investigated and discussed on the basis of the impregnation parameters. The present work showed that process parameters (pressure and temperature), polymer impregnants (different molecular weight polyethylenes), and wood species contributed significantly to PR and H-B. Increasing pressure and temperature resulted in a higher PR and H-B, whereas increasing the molecular weight of polyethylene and switching wood species from aspen to red maple gave a lower PR and H-B. This study was aimed at understanding how impregnation parameters affect the final properties of wood plastic composites and developing an optimal fabrication process for wood plastic composites. (c) 2006 Wiley Periodicals, Inc.