The stress-weight ratio has often boon used to make such comparisons. This is permissible with the simpler types of loadings, such as pure tension or compression, but as more complicated 1oadings are encountered the ratio gives fallacious resu1ts. Some types of stresses depend entirely on the ratio of Young’s Modulus to density, others on a function of the stress-weight ratio and a dimension. It can be seen from those facts that using only the stress-weight ratio for comparison does not always lead to a correct evaluation of the weight efficiency of a material.