Handmade Persian rugs possess a high level of quality, durability and investment value which machine made rugs can never match. While a machine rug made wears down after ten or twenty years and needs to be replaced, a handmade rug will still be considered new and show few signs of wear, if it has been properly cared for. In fact, a handmade rug can last for generations in the same family! Handmade rugs are an ancient, sophisticated peasant or nomadic folk art and handicraft that is associated with Persia or modern Iran, and they are also woven in Afghanistan, Pakistan, Turkey, India, China, the Caucasian region and central Asian region in and around Turkmenistan. Handmade rugs have also been made in rug weaving workshops on larger scale and with more refined and complex patterns for royal palaces and for export. Handmade rugs are primarily made of wool, cotton, silk. Some rugs of lower quality use materials, such as jute and animal hair (goat, yak, camel). The finest grade of material is kurk wool, which is made from lamb wool shorn from the shoulders and chest, along with silk; such rugs will be the most expensive. The fineness of kurk wool and silk allow for a very dense weave, which in turns allows for very refined and detailed designs to be made. One measure of rug quality is regarded as the number of hand-tied knots per square inch of the rug: an average is 150, fine rugs have 500 knots per square inch, and this figure can reach even up to 1,200.