Genuine Persian or Oriental rugs are hand-woven and have natural materials and fibers in the foundation like cotton, wool, silk, goat or camel hair and jute. In some cases, these materials are combined together. In general rug foundations, wrap and weft are made of cotton, but there are weavers like Turkmen, who use it for creating contrast in the color of the rug design.
Cotton has many advantages when used as a basic material, but it has to be natural and not mercerized. When natural, this fiber is strong, allows excellent weaving and does not lose its shape. Cotton is grown in the regions where rugs are weaved. Meanwhile, weavers in areas where cotton is not produced use wool for wrap and weft. The oldest carpet in the world, the Pazyryk rug is made of wool. This excellent fabric that remained buried for about 2,500 years has a wool warp, weft, and pile. But wool is not a good choice for the foundation material of larger rugs. It tends to shrink when washed and can fail to lie flat on the floor.
Most Oriental and Persian rugs are made of wool on a cotton foundation. But there are even cases of wool on silk, silk on silk and wool on wool. Wool is the strongest fiber used in carpet weaving because it is great for hiding dust and dirt. Thus, wool carpets look better and need to be cleaned less often. Tribal weavers use camel or goat hair in their rugs. This can be an indicator that the rug is authentic, but excess use of these materials are unappealing to buyers.
On the other hand, rugs made of goat and camel hair are difficult to dye and loss colors faster than wool rugs. The wool used for Oriental and Persian rugs is of high quality and comes from the mountainous areas of Central Asia or from Australia and New Zealand. Wool is also a green choice while other non-natural fibers and materials are made petroleum by-products.
Further on, silk is a strong but expensive material. Therefore, silk rugs are weaved only in urban areas, because tribal craftsmen cannot afford it. Tabriz rugs are the most famous when it comes to silk carpets. They are beautiful and of good quality and are used for decoration purposes.
In a nutshell, cotton remains the best choice for carpet foundations. It is natural, strong and not expensive.