longer on the market. Nylon Nylon is the most popular string material for amateur players due to its low cost and the improvement in elasticity offered by multi-filament strings. Wear-resistant coatings for nylon strings are common, especially with multi-filament strings, because the outer filaments tend to break first as the racquet is used. Polyester Polyester is a stiff and durable string material, originally intended for use by frequent string breakers. It took time for this string material to become popular, primarily due to its poor tension holding capability. However, players feel they are able to apply more topspin to balls while maintaining control with polyester strings. Polyester revolutionized professional tennis when a then little known Belgian string maker Luxilon supplied Gustavo Kuerten in 1997, who went on to win that year's French Open. Since then, polyester's support for heavy topspin in particular has made it the most popular string material in the professional tennis tour. The increased topspin due to polyester strings has been verified with controlled experiments today. The exact cause for the increased spin is not known but there is strong evidence that the low friction between strings is a factor. Kevlar Kevlar is the stiffest, most durable synthetic string available, and is thus extremely hard to break. Although it is one of the best strings in terms of tension holding capability (next to natural gut), it is the most dangerous string when it comes to developing tennis elbow. Kevlar is often strung with another string, such as nylon), in order to combine both strings' qualities, as Kevlar by itself feels too stiff for many tennis players, especially when combined with a stiff racquet. Some advocate using a very thin gauge Kevlar for increasing comfort, but even in the thinnest gauge it is a stiff string. Another strategy to increase comfort and improve rebound efficiency is to string Kevlar at a low tension. Vectran Vectran is the second-most stiff and durable of string types. It is perhaps the least commonly used contemporary string material. It is usually added to nylon string to increase nylon's durability and stiffness, as with Kevlar. Yonex, for instance, offers two badminton strings, made primarily from nylon, which have Vectran strands. However, the Ashaway company offers a braided Vectran tennis string. Zyex Zyex string offers more rebound efficiency, i.e. gut-like dynamic stiffness, than other synthetic strings, particularly when strung at low tensions. This gives