A foam composite with a skin 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 as a core, and a covering of a reinforcing member for the core.