Virtual reproduction of optical material properties is an important task for many computer graphics applications. Recently, bidirectional texture functions (BTFs) [Dana et al. 1999] have become quite popular for photo-realistic rendering of surfaces. BTFs can represent a huge variety of different materials. They can be easily integrated into any modern rendering system which offers programmable surface shaders. BTFs of real materials can be optically measured, they are known to be efficiently compressible and can be used for real-time graphics rendering applications even on the web using WebGL.