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1)    What is synthetic gut?

The string commonly known as synthetic gut is made of nylon and is constructed in the way shown in the picture on the right. That is, the string is composed of a solid nylon core surrounded by a single wrap of thinner filaments. A coating of silicone is applied to reduce friction. As the name implies, this type of string was developed to simulate the playing characteristics of natural gut.

2)    What are the main attributes that distinguish different types of strings?

The material used in a string (for example "nylon" in the case of synthetic gut), the construction of the string (a solid core surrounded by a single wrap of thinner filaments in the case of synthetic gut), and the gauge, or thickness, of the string define the essential characteristics of a string.

3)    Do different brands of string play differently?

Strings of same material, construction and gauge have very similar playing characteristics regardless of the brand name they are sold under. Although string companies go to great length to create a distinctive image for their strings, the results of scientific tests published by the USRSA (United States Racquet Stringers Association, June and July, 2000 issues of Racquet Tech ) demonstrate that the material, construction and gauge are a lot more important than string brand in determining the playing characteristics of a string. Among these three variables, the material that a string is made of is by far the most important in determining the playing characteristics of the string.

4)    Since the material a string is made of is so important, what materials are there to choose from?

The most common materials for tennis strings are natural gut, nylon, polyester and kevlar. USRSA tests revealed that the dynamic stiffness of a string (think of this as the elasticity of the string after it has been tensioned) "determines almost everything" in the playing characteristics of the string. The less stiff a string is, the better it plays. Natural gut is the least stiff string material, followed by nylon, polyester and kevlar. While natural gut is the least stiff string material, nylon is not far behind, and polyester is a bit stiffer still. Kevlar, however, is way stiffer than any of the other materials, so one takes a bigger jump into stiffness when going from polyester to kevlar than when going from natural gut to nylon or from nylon to polyester.

5)    If natural gut is best, why doesn't everyone use it?

Natural gut is undeniably the best string a tennis player can use, and the majority of top professional players do use it. Unfortunately, natural gut is very expensive, the price for a coil for stringing one racquet ranging from $25 to $35 (by mail order). The reason natural gut is so expensive is that it is made from cow or sheep intestine and requires a lot of labor to turn into string. Long strips of intestine are cleaned to expose the collagen sheath known as the serosa, they are then cut into strips, dried in salt for several weeks, twisted together to form a string which is put in a drier for about a day and is then covered with a protective polyurethane coating and finally packaged. The elasticity of natural gut apparently derives from the need for the intestine to expand dramatically when accommodating a big meal, and then to contract after digestion. The best known brand of natural gut is Babolat VS (you have noticed the logo consisting of two lines near the throat of professional tennis player's racquets). Pete Sampras used it and was reputed to have had his racquets restrung before a match whether the strings have been used or not! Natural gut has gradually lost a lot of its popularity with top players and Silent Partner does not sell it.

6)    Given that natural gut is too expensive for most players, how does one choose a less expensive string?

Earlier we saw that string commonly known as synthetic gut is made of nylon and has a construction consisting of a solid core surrounded by a single filament wrap. The reason synthetic gut is the most commonly used string in tennis is because nylon is only a little stiffer than natural gut, and the solid core/single wrap construction is inexpensive to produce. In a nutshell, synthetic gut achieves an excellent balance between quality and price. One can increase the elasticity of a nylon string by using a different construction. Instead of having a solid core surrounded by thin filaments, the string is constructed entirely of thin nylon filaments. These are known as multifilament strings and USRSA tests show them to come closer in elasticity to natural gut than solid core/single wrap synthetic gut. The picture on the right shows the multicore/single wrap construction of Silent Partner Filament Frenzy. The single wrap of slightly larger filaments is used to enhance durability because multifilament strings are not usually as durable as synthetic gut. The USRSA tests mentioned above have shown that strings with this multicore/single wrap construction are as elastic as strings that are composed entirely of thinner filaments. Multifilament strings (with or without an outer wrap) cost more than solid core strings, but they offer improved playability.

7)    If natural gut and nylon offer excellent elasticity, why are some strings made of polyester or Kevlar?

Elasticity (or low dynamic stiffness) is a property that contributes to the playability of a string. The other important characteristic of a string is its durability. Natural gut and nylon strings offer acceptable durability for most players, but hard hitting players usually break them in a few hours of play. Polyester and Kevlar offer much better durability at the expense of increased stiffness. Polyester resists notching where strings cross, and therefore lasts longer than nylon (at least three times longer, in our experience). Polyester is usually extruded as a single thick filament (outer wraps do not adhere to polyester) and polyester is the only true "monofilament" string available for tennis. Kevlar is the registered trademark for Dupont's famous material that bullet proof vests are made of. Generically, strings like Kevlar are known as aramids (Technora is another aramid string). Aramids provide outstanding durability (perhaps five or more times the durability of nylon), but they are extremely stiff.

8)   I am a "string breaker". What's my best choice of string.

Silent Partner recommends polyester over Kevlar. This is because polyester's dynamic stiffness is nearly as low as that of nylon, and its durability is nearly as high as that of Kevlar. Polyester, therefore, offers an excellent compromise between playability and durability. Also, whereas Kevlar is a particularly expensive synthetic string material, polyester is among the cheapest. Silent Partner sells polyester as well as Kevlar strings.

9)   I need the durability of polyester or Kevlar, but I do not want my racquet to feel stiff like a board. What can I do?

Stringbed stiffness (the stiffness of the entire stringbed rather than of individual strings) can be reduced in a number of ways, even when very stiff strings like Kevlar are used. The main contributor to stringbed stiffness is the tension at which the racquet is strung. One way to reduce stringbed stiffness is to reduce tension. It is often recommended that a player adopting Kevlar for the first time reduce tension by 10% compared to prior stringings with nylon. Polyester does not require nearly as much of an adjustment. The main other way that stringbed stiffness can be reduced is by using a "hybrid".

10)  What is a "hybrid" string job and how is it achieved?

A hybrid consists of a stringbed with a different string for the "mains" (strings that run lengthwise in the racquet head) and the "crosses" (the shorter strings that run at a right angle to the mains). Hybrids are often used to maximize durability while keeping stiffness as low as possible. Because mains usually break before crosses, a durability oriented string such as polyester or Kevlar is used for the mains while a more elastic string is used for the crosses. Silent Partner recommends that a 17 gauge synthetic gut be used for the crosses when polyester is used for the mains and that an 16 gauge synthetic gut be used for the crosses when Kevlar is used for the mains. Interestingly, for most of his career Andre Agassi used Kevlar for the mains and natural gut for the crosses. This is an unusual combination that worked for Agassi because a hard hitter like him wants the durability of Kevlar and is not concerned about the cost of natural gut in the crosses.

11)  Are hybrids ever used for reasons other than maximizing durability and minimizing stiffness?

Hybrids can be used to maximize playability while keeping cost low. Because the mains are the longest strings in a racquet, and because string length is an important determinant of the playability of a stringbed, it makes sense to install the most playable string in the mains. For example, a player who wants the playability of natural gut will get most of the benefits of natural gut by stringing the mains with it while stringing the crosses with an inexpensive 17 gauge synthetic gut. This cuts the cost of a string job with natural gut in half while providing playing characteristics that are practically indistinguishable from an all-gut string job. Andre Agassi's Kevlar/gut hybrid is unusual because most players would not notice the qualities of natural gut when it is used for the crosses. Andre Agassi's sensitivity to the properties of a stringbed are, of course, not those of the common player.

12)    What is the gauge of a string and how should it be chosen?

The gauge of a string is its thickness. Tennis strings range from 15 gauge (about 1.4mm) to 18 gauge (about 1.1mm). "L" in a string gauge such as 15L refers to a slightly thinner variation of that gauge (so 15L is between 15 and 16). The most common string gauge for synthetic gut in North America is 16, but players looking for durability can choose a thicker string such as 15 or 15L, while players looking for more elasticity can choose a 17 or 18 gauge string. The gauge of string has a major influence on its elasticity and playability. The USRSA reports that a 17 gauge string is about twice as elastic as a 15 gauge string of the same material and construction.

13)    What is the most elastic and playable synthetic string?

The most elastic synthetic string has a thin gauge (such as 18 gauge) and is made of an elastic material (such as nylon), using a construction that promotes elasticity (such as a multifilament construction). Few players use 18 gauge strings, especially for the mains, because they would break too quickly. Even 17 gauge string is not very durable when used in the mains. But a 16 gauge multifilament nylon string is a very good choice when the emphasis is on elasticity with acceptable durability. Silent Partner's Filament Frenzy falls in this category.

14)  What string characteristic contributes to power?

The conventional answer to this question is that the more elastic the string, and the lower its tension, the more power it generates because of a trampoline effect. This notion is correct, though it oversimplifies the issue a little. This is because when a ball hits the stringbed, the strings deform like a trampoline, but the ball also deforms. This dual deformation reflects the storage of energy (from the hit) in the stringbed as well as in the ball. The stiffer the stringbed, the less it deforms, but the more the ball deforms. The looser the stringbed, the more it deforms and the less the ball deforms. The important question is, how much of the energy stored in the stringbed and in the ball is reimparted to the ball as it leaves the stringbed? Because strings regain their shape faster than balls, more of the energy stored in the stringbed is reimparted to the ball than energy stored in the ball (the ball leaves the racquet before totally regaining its shape, and this results in a loss of energy). So it should be true that low string tension results in more power than high string tension. If this is not complicated enough, consider that recent tests and calculations published in the USRSA magazine (in particular an article by Professor Rod Cross in Racquet Tech, September, 2000) suggest that string tension and elasticity have negligible effects on power (that is, Kevlar strung at 65 LB generates the same power as natural gut strung at 55 LB). This is a rather controversial claim that flies in the face of years of player experience, and Silent Partner endorses this claim only after clarifying what "negligible" means. Silent Partner has conducted tests comparing natural gut to Kevlar strung at 60 LB. Balls were shot by a ball machine at a stationary racquet head. Test conditions were carefully controlled, the identical racquet and string tension was used in the two tests. Balls shot at the natural gut stringbed rebounded 7% farther on average than balls shot at the Kevlar stringbed. The difference was statistically significant an represented what would amount to a difference of several feet in where a blocked serve would land on the server's side. So, one physicit's "neglibible" difference may be a player's "OUT" call. In a game where differences of mere inches determine whether a ball is in or out, the differences observed in Silent Partner's tests were substantial. The position taken by Silent Partner is that empirical tests with criteria that are related to call outcomes need to guide the choice of labels used to describe the differences caused by variations in string tension.

15)  What string characteristic contributes to control?

Control is the flip side of power. Advanced players who hit with full swings and high racquet head speed do not have trouble generating pace. For them, keeping the ball from flying farther than they wish is of greater concern. The problem with the trampoline effect discussed in Question 14 is that it is not under tight player control, and it creates more variation in where the ball goes than pace generated by the swing itself. For this reason, advanced players prefer tight stringbeds that do not introduce variability due to the trampoline effect. Perhaps a good analogy is with a sports car that keeps the driver in more direct contact with the road, much like a tight stringbed keeps the player in more direct contact with the ball. So how can one promote control? Primarily by stringing at a higher tension (did you know that Bjorn Borg was sometimes woken at night in his hotel room by the sound of strings snapping spontaneously? His racquets were strung at more than 80 lbs!). Another approach is to use a stiffer string like Kevlar, though subjectively such stiff strings are not as "playable" as more elastic strings, and this is probably the reason that they are seldom used by professional players.

16) What string characteristic contributes to playability?

Playability is a highly subjective impression about strings that is generally related to the elasticity of the string. So strings that generate power (like natural gut or multifilament strings) tend to also be playable. Little is known about the exact characteristics that contribute to the subjective impression of playability, but along with elasticity, the gauge of the string as well as the finish applied to it during manufacturing seem to be factors.

17) What string characteristic contributes to spin?

The texture of a string contributes to its ability to generate spin. A thicker filament is spun around the core of spin oriented strings like Silent Partner's Headspin in order to create a texture that bites into the ball. The gauge of a string also contributes to spin, thinner strings having a better ability to bite into the ball. Perhaps the most important equipment factor that contributes to spin has nothing to do with the string itself. It consists of the "string pattern" or the density of the checkerboard pattern formed by the strings. Open string patterns, consisting usually of 16 mains and 18 crosses configured so that the strings sit far from each other, allow the ball to imbed itself more in the string bed and this causes the main strings to brush more effectively against the ball.

18)    Why do strings break?

The primary reason strings break is that "main" strings rub against "cross" strings when the ball is hit with spin. Gradually, this rubbing cuts a notch in the main string. When the notch gets deep enough the string cannot withstand the stretch caused by a strong shot, and it breaks. The thicker the string, the deeper the notch it will tolerate before breaking. That's why thicker strings last longer than thinner strings. The more abrasion resistant a string is, the longer it will take for a notch to grow. This is why polyester strings last longer than nylon strings. The higher the tensile strength of a string (the tension it can withstand without breaking) the deeper a notch it will tolerate before breaking. This is why Kevlar is very durable. Another factor that contributes to string wear is the abrasiveness of court material that is picked up by the ball and deposited on the strings. That's why strings break more quickly on clay courts than on hard surfaces. Rallies also tend to last longer on clay courts, and the corresponding increase in hits during a match contributes to string wear. Notching is not the only reason for string breakage. A ball hit near the frame can cause a shear break, even on a new string. Strings that are damaged during stringing can also break prematurely. So can strings that are installed in cracked or damaged grommets.

19)  Can anything be done to make strings last longer?

The only effective method for extending the life a strings during play is the insertion of little plastic pads at the cross points between main and cross strings, especially in the area of the sweet spot. These inserts work by reducing the notching effect that the crosses have on the mains. You have seen professional tennis players insert these during matches. The most popular inserts are made by Babolat and are called ElastoCross. Although these inserts do extend the life of strings, many players who have used them do not find that they are worth the cost (about $6 for the applicator and inserts) and the trouble (it takes time to install the large number of pads necessary to protect the vulnerable strings in a stringbed, while waiting and protecting only the strings that fray reduces the effectiveness of the approach). The pads can also be a nuisance because they can fall on the court during play, and they need to be contained in a plastic bag when old strings are removed from a racquet.

20)  How often should strings be replaced if they are not broken?

The rule of thumb is that strings should be replaced as many times a year as one plays in a week. Why should one replace strings before they break? Because two things happen to tensioned strings over time. The first is tension loss. For example, a freshly installed synthetic gut will typically lose close to 10% of its tension within 24 hours. The rate of tension loss drops substantially after this, but it is still a factor and its impact can be felt, especially months after strings have been installed and hit with. Some players think that their racquet becomes more powerful because of the enhanced trampoline effect created by the loss of tension. This is probably a misconception because of something else that happens to strings over time. The second thing that happens to strings over time is that they lose their resilience (think of it as zing, or the string's ability to reimpart energy to a ball quickly after being deformed by a hit). This loss of resilience comes across as string fatigue, or the feeling that the strings are dead and mushy. For these two reasons, therefore, strings sometimes need to be replaced before they break. You may wonder if some strings lose their tension faster than others. The answer is yes. Multifilaments lose their tension faster than synthetic gut (monofilament with one wrap). Polyester is also reknowned for losing its tension relatively fast (Silent Partner only sells polyester in 17 gauge because it is very durable and will need to be replaced for reasons of tension loss if not for breakage. There is no point, in other words, going for the extra durability of 16 gauge or 15 gauge polyester).

21)  What is the shelf life of string?

Strings made of synthetic material can last several years in their original packaging without noticeable change in their playing characteristics. This assumes that extremes of temperature and direct sunlight are avoided during storage.

22)  I have tennis elbow, what string should I use?

Players who suffer from tennis elbow, or any other form of arm or shoulder tendinitis, should do everything they can to reduce the stiffness of their racquet's stringbed. This means selecting the most elastic string possible, such as natural gut or a nylon multifilament, using a thin gauge of that string, and reducing the tension at which the racquet is strung. One should not count on these measures alone to cure tendinitis. The advice of a doctor should be sought.