· The interest in composites can be understood from the plot of Young's modulus versus Density shown. 
· The green field is associated with composite materials and the line of constant (E/ρ) passes through materials that have similar structural efficiencies in a tensile loading situation.
· Guide lines for constant (E/ρ²) and (E/ρ³) pass through materials suitable for cantilever, or compressive loading use at minimum weight.