A class of lightweight structural members, characterized by lighter weight and greater resistance to buckling under axial compressive loading, as compared to conventional structural members, is described. The lightweight structural members typically comprise a thin tubular member filled with a metallic foam material. The foam material preferably comprises particulate matter comprised of agglomerated fly ash material, and, preferably, gaseous material in pores within the foam material.In an alternate configuration, the lightweight structural member comprises two tubular members, one nested inside the other, wherein the annular volume between the tubular members is filled with metallic foam material.A method for manufacturing the structural members is also described.