Violin strings can be made of different materials, including gut, steel, and synthetic polymers. Historically, most bowed instrument strings, including violin strings, were made from animal intestines, such as sheep or cow intestines. These strings are often referred to as catgut strings, but they were never made from cat intestines. Nowadays, most violin strings are made with steel or synthetic materials. Authentic gut strings are still used by some advanced professional violin players, including those who specialize in historical performance, but they are not the norm for the average violinist. The types of metals used in the core of the strings affect the sound quality, and whether the core is made of a solid metal, stranded metal, or synthetic polymers also makes a difference. The outer layers of violin strings can be coated or wound with different materials, such as aluminum, silver, gold, or tungsten, which can also affect the sound quality. Ultimately, the choice of violin strings depends on personal preference and price range.