In a part-18 file for an HD texture pack, you would likely find:
Since "HD-Texture-Pack.part18.rar" is typically one piece of a large, split archive, the content inside is usually a continuation of high-resolution image files and configuration data. HD-Texture-Pack.part18.rar
: Texture layers that define how light interacts with surfaces to create the illusion of 3D depth and bumps without adding polygons. In a part-18 file for an HD texture