A physically based hair BSDF I implemented for the open source renderer Mitsuba as part of my master's thesis. The basic model is by Marschner et al. "Light Scattering From Human Hair Fibers", with improvements from d'Eon et al. "An Energy-Conserving Hair Reflectance Model" and Zinke et al. "Light Scattering From Filaments". The images in the slide-show are unmodified rendering results under very basic lighting.
Date: May 2015