**1. Introduction**

Textile and nonwoven industries are fiber-based industries. They use both continuous fibers as filament yarns and/or short fibers as staple fibers. During the manufacturing processes, these fibers, very thin 1D elements, are transformed in oriented or random 2D laps or webs. Then, these products are converted in 1D end product as staple yarns or 2D end products as woven or knitted fabrics or nonwoven fabrics. The physical and mechanical properties of these end products strongly depend on the regularity of laps or webs. Therefore, an accurate knowledge of the web and lap formation as well as the associated theoretical approach are absolutely necessary.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
