Porous materials have attracted attention because they exhibit a wide range of useful properties. They are mainly manufactured using either a precursor or a melting method. However, the processes involved are complicated because of the need for a primary extrusion step and the addition of a pore-forming agent. Also, because of the large amount of energy required for the sintering step, these methods represent a large environmental burden. To solve this problem, the present study focused on the formation of solidified porous aluminum by a reaction between pure aluminum powder and pure water, without the need for sintering. The effect of the formation temperature was investigated by measuring the amount of hydrogen released during the reaction, and the density and microstructure of the final materials. X-ray diffraction measurements and compression tests were also carried out. The results of the microstructural observations and X-ray diffraction measurements indicated that, during the reaction, a bayerite layer was formed on the surface of the powder particles. With increasing temperature, the reaction was found to start more quickly and more hydrogen was released. Furthermore, from the compression tests, the initial maximum stress, the plateau stress and the absorbed energy decreased with increasing formation temperature. The results of the present study indicated that it was possible to form highly porous aluminum using the proposed method.