Abstract: Neutron shielding material in the form of a thin rigid sandwich, comprising outer layers of metal, preferably aluminum, and a solid core formed of a uniform intimate solid mixture of particles of metal and a neutron absorbing material, preferably boron carbide (B.sub.4 C). The sandwich is made by initially forming an open-sided welded box from metal plates, preferably aluminum, leaving one end open. Uniformly and intimately mixed particles of the metal powder, preferably atomized aluminum, and the neutron absorbing material, preferably boron carbide having an approximate range of 20-200 mesh particle size, is placed in the box so as to completely fill it, and the open end is closed by welding another metal plate in position. Openings are provided in the ends of the box for the escape of air, the box is heated to approximately 800.degree.-850.degree. F., and is then rolled to required thickness, as for example 0.125 or 0.250 inch.