Think of the "Highlight Size" slider in the Surface Material dialog box as being better named: "Highlight Diffusion". A low value on this slider yields a sharp, focused pinpoint highlight as one would see on a very shiny surface, versus a high value on this slider which produces a broad, diffused highlight as one might see on a more rough, dull, or generally less reflective surface. IMHO: approx 75%=dry skin; 50%=moist skin; 15%=wet skin