There are numerous ranges of yarns, which differ in several ways. The simple yarn is made up of a single head, a single colour, with a single count (weight) and number of twists. There are also twisted yarns, obtained by joining two or more simple yarns, equal or different. From the simplest combination of two yarns it is possible to create the most complex of twisted varieties. The knowledge of the twisted and the large number of effects obtainable with them is critical in the design phase of the tissues. The knowledge of twisted threads and the large number of possibilities obtainable with this technique is essential when designing the fabrics.