Plastic foam has excellent heat insulation properties, however, moisture absorption is causing a decrease in the heat insulation, and plastic foam has almost no mechanical strength. Therefore, a heat insulation material that absorbs almost no moisture and has satisfactory strength is desired to appear. According to the present invention, a foam composite with a skin can be formed in one shot by charging plastic powders or minute particles together with polyolefin pellets that can be cross-linked and foamed in a mold, and heating the mold while rotating. The composite absorbs almost no moisture, having satisfactory strength, being excellent as an insulating material. Further, providing a covering of a non-foaming or a slightly foaming material to the pellet of polyolefin that can be cross-linked and foamed, and conducting the forming, foamed granules of preferably 5 to 50 mm largeness as a core, and a covering of a reinforcing member with 0.05 to 0.5 mm thickness for the core, can be formed, which permits that thus obtained shaped body is lightweight, strong, with an equivalent strength to wood that undergoes deformation without breaking when subjected to impact.