Wood could provide better service in some applications if it were harder and more dimensionally stable. In this study, wood-polymer composites (WPC) made with different chemical combinations were evaluated for dimensional stability, ability to exclude water vapor and liquid water, and hardness. Pine, maple, and oak solid wood were combined with different combinations of hexanediol diacrylate, hydroxyethyl methacrylate, hexamethylene diisocyanate, and maleic anhydride. Treatment slowed the rates of water vapor and Liquid water absorption. Although the resultant dimensional stability was not permanent, the rate of swelling of WPC specimens was less than that of unmodified wood specimens. In addition, WPC were harder than unmodified wood. The chemical combination of hexanediol diacrylate, hydroxyethyl methacrylate, and hexamethylene diisocyanate greatly decreased wetting and penetration of water into the wood. This chemical combination also gave the hardest and most dimensionally stable WPC. In general, WPC prepared using hydroxyethyl methacrylate were harder than specimens made without hydroxyethyl methacrylate and excluded water and moisture more effectively.