In the DIRSIG world, everything is assigned a "material". A material is the central method that is used to assign both optical and thermal properties to an element in the DIRSIG world. Therefore, understanding how materials are managed, where they are defined, how they can be defined, etc. is an important aspect of understanding the DIRSIG model.
Since this is one of the core aspects of the DIRSIG model, you will find that this general topic has been divided across several chapters. This chapter discusses the basics of material management within the model. The next chapter, entitled "Property Mapping Techniques", discusses some advanced techniques for applying materials to scene elements and introducing variability within a material (e.g. "texture"). Finally, the chapter entitled "Thermal Modeling" discusses the complex topic of thermodynamic modeling supported by the DIRSIG tool.