One can characterise a surface that has undergone certain finishing operations by three main properties of: roughness, waviness, and fractal dimension. Among these, roughness and fractality are of most importance, with roughness often indicated in terms of a rms value, σ σ and surface fractality denoted generally by D f. The effect of surface structures on thermal conductivity at interfaces is analogous to the concept of electrical contact resistance, also known as ECR, involving contact patch restricted transport of phonons rather than electrons.