These are an extension (and improvement) on nylon strings, which were brought out few years ago, to compensate for the lack of durability from natural gut. The classic example is Prince Synthetic Gut. The majority of factory strung rackets are strung with synthetic guts, and are a good choice for most people. They give a good mixture of power and control with a "crisp feel and sound". They do not offer much potential for spin, however, unless you go for a "textured or spin" type. They are also available in a variety of different colours. Synthetic strings are good on their own, or in combination with more durable kevlars and polyesters.