To provide a method for producing a structural material, having large specific surface area, having a porous integral structure distributing to porosity and load resistance/air permeability/water-retaining property from the outside, having both of the container functionality and the floatability regardless of kind/hardness/density of the fiber, capable of repacking a packing layer of the inside of the structure and being usable for multipurpose application, e.g. contact filtration/catalytic material.

A fiber aggregate and an uncured FRP material are formed in sandwich state and both materials are fixed in three-dimensionally entangled by a needle. When curing of a FRP layer finished, a fiber aggregate layer is strongly protected and a porous volume body having an integral structure, e.g. tough egg shell is obtained. The volume body is excellent in load resistance as a container. Repacking of filler (3') of a interior part is made arbitrary and selection of new or waste materials is made possible every purpose/application by providing a through hole in the volume body. As a result, resource can be saved and labor can be saved and control for exhibiting flotation characteristic can be carried out.