The cities of central Iran, Teheran, Isfahan, Kashan, Yazd and Kerman, are known for the beauty of the Persian rugs that they produce. Many of the region's smaller towns and villages—Veramin, Tafresh, Boroujerd, Khomaine, Taleghan, Najafabad, Josheghan and Maymeh, Yazd and Ardekan—are also well-known for the high quality rugs that they produce. Kashan and Isfahan, key Persian rug-weaving towns since the 16th century, have had an enormous impact on the industry throughout their regions. Yazd and Ardekan rugs feature Kashan designs and Najafabad ones use Isfahan patterns. It can take weavers in these cities years to weave one of their rugs. The rugs woven in the towns and cities of central Iran use the asymmetrical Persian knot. They are made of wool, silk or a combination of the two. The foundations are usually cotton, but silk is sometimes used in the finest pieces. Many of the region's rugs have been known to last for hundreds of years.