Cubic materials are special orthotropic materials that are invariant with respect to 90° rotations with respect to the principal axes, i.e., the material is the same along its principal axes. Due to these additional symmetries the stiffness tensor can be written with just three different material properties like
The inverse of this matrix is commonly written as
where  is the Youngs modulus,  is the shear modulus, and  is the Poissons ratio. Therefore, we can think of the ratio as the relation between the shear modulus for the cubic material and its (isotropic) equivalent: