The effective conductivity of binary composites may be estimated through a number of analytical, empirical and numerical methods. These methods must incorporate the relative conductivities, the volume fractions and morphologies of the constituent materials. The concept of microstructural efficiency is introduced in this paper as a means of quantifying the effect of morphology on effective conductivity in a composite. The variation of microstructural efficiency on structured prismatic and three dimensional morphologies is calculated using a Lattice Monte Carlo method. This information enables discussion of the advantages and disadvantages of particular morphologies as conductors or insulators in addition to providing a method for calculating effective conductivity. (C) 2014 Elsevier Ltd. All tights reserved.