The application of the WPC as building material requires that they are used outdoors and are often exposed to moisture. The intrinsically large numbers of pores in the foamed WPC structure have hence become an issue of concern when the foamed WPC are used in wet areas or outdoor sites with constant exposure to water. Bledzki and Faruk [9] reported 25 % water absorption and 7.5 % swelling of the
foamed polypropylene/wood composites after having been soaked only 12 days. Kord [6] found that the water absorbed by the high-density polyethylene/rice hull composites increased with the addition of CBA. Iulianelli et al. [11] observed a reduction of the impact strength in the soaked PVC/wood flour composites.