cotton is cellulose fibers obtained from cotton pod (boll) which, after spinning and changing it to yarn, is used in wrap and weft of carpets. Due to high cost of wool yarn and strength of cotton yarn and also its lesser culicue compared with wool which prevents a sort of laxity of the carpet, in carpet-weaving cotton yarn is used as wrap.Another advantage of cotton yarn used in carpets is resistance to moth pest because moth is not interested to eating cotton; therefore when the carpet is attacked by such pests only the piles are lost and it will be easier to repair it.Amongst the factors influencing the cotton quality, color, impurities and quality of purification can be mentioned. Based on climatic conditions, length and thickness of cotton fibers may vary. The longer its fibers and the lesser its thickness, the higher will be its quality.Amongst the characteristics of high quality cotton, its higher length, lesser thickness and its white color can be mentioned.A point worth considering is that sometimes viscous fibers are used as wrap or weft which leads to decreased quality of the carpets woven of such materials. 

 
Procedures of identifying cotton
A-    By burning cotton yarn
Once contacted with flame,  cotton rapidly burns and after being away from the flame it becomes extinguished and leaves a soft powdery ash.
B-    Physical observation :
Under microscope, cotton fibers seem to be longitudinally twisted and spun and from the transverse section view they seem bean-like.
C-    Chemical procedure :
Cotton is not resistant to acids, and substances such as sulfuric and hydrochloric acids completely destroy it.

Important Center of Production

Amongst important centers of cotton production in Iran we can mention the cities of : Azaerbaijan, Gorgan, Khorassan, Guilan and Mazandaran, Isfahan, Yazd, Kerman and Gonbad Kawoos.
Production of Cotton Yarn

Cotton yarn is produced by two procedures : either by machine or by hand. In hand spinning procedure, cotton is spun either by hand or with the aid of the spinning wheel. This type of yarn is thicker than the machine-woven yarn, shows discords along its length, and is cheaper, and is usually used in weaving rural low cost carpets.

In the instrumental (machine-made) method, the cotton in spinning factories is changed by machine spindles to yarn. This type of yarn is finer and more uniform than the hand-spun yarn, therefore it is more expensive and in weaving civic and semi-rural high quality rugs and carpets machine-made yarn with standard diameter is used.

Grading (Numbering) of Silk Yarns

For grading silk yarns the denier system is employed which is the weight of 9000 m silk fiber/gram. Conversely to metric number, the higher the denier, the thicker will be the silk fiber. In carpet-weaving, deniers 60-160 are common and deniers 60-80 are used for wrap and deniers 100-160 are employed for carpet flowers.

                        Den = W/L x 9000