String Power: Comparing Zyex® and Nylon
By Steve Crandall
Vice President, Sales & Marketing
Ashaway Racket Strings
One of the difficulties in talking about string is that we have no common frame of reference. When someone says it's 25°F outside, you know you should probably wear a coat. Conversely, if someone says they "fried" themselves at the beach, or "overindulged" at dinner, you also have a fairly accurate idea of what they mean. But when we talk about racquet string, we not only have no convenient numerical standards, like temperature, but even qualitative descriptors like "durability" and "playability" mean different things to different people.
At 145 lbs./in, the dynamic stiffness of Zyex is the closest to gut of any synthetic string material. It has even been called the "space age nylon." This means it absorbs and returns impact force better than nylon. We call this "Soft Power" with our UltraKill® 17 and 18 gauge strings; "Ultra Power" with heavy-gauge UltraKill 16. It controls the ball better than nylon, especially in thinner gauge strings, and holds tension much better than nylon, which means it stays playable in your racquet longer.
This lack of common reference can be especially difficult when we're not just talking about a specific string, but a string material - like Zyex®, which has gotten a lot of attention lately - or even a method of constructing string that can be applied to a whole range of string products.
One way to get around this difficulty is to compare a new string or material with another string or material whose characteristics are better known. Crawford Lindsey, Rob Cross, and company at USRSA (RacquetTECH.com) have been doing some very interesting studies to measure string performance which, one day, may well result in a standardized rating scheme for all strings. Their work is highly technical, but some of their comparison data may help us shed light on the differences between nylon and Zyex in generating power.
To do so, it will be helpful to compare these materials to natural gut. While never used in racquetball to my knowledge, gut has long been the "gold standard" in tennis, as it has a number of properties that make it ideal for racquet strings. Made from the intestines of cows (not cats!), its performance has been unmatched since it was first introduced in the nineteenth century. What makes gut a superstar is its ability to stretch on impact and then rebound quickly without deformation or loss of tension. This means several things: 1) the string absorbs the force of impact, not the racquet or the player's arm. In other words, gut plays "soft;" 2) it returns that force to the ball very quickly and efficiently, providing more power; 3) because it stretches, it allows the ball more dwell time on the strings. This lets players "pocket" the ball and enhances control; 4) gut maintains tension over the life of the string, enhancing its value. Gut is also quite durable when struck on the sweet spot, but not so much on off-hits, making it better for better players. On the downside, gut is very expensive and, without protective coatings, tends to sag in high humidity.
The key to gut-like playability is dynamic stiffness, which can also be likened to elasticity. Zyex inventor Bruce McIntosh calls dynamic stiffness "the ability of a material to resist stiffening up as it is rapidly stretched and released - to become 'boardy.'" It's measured in pounds per inch, and in laymen's terms, is a measure of how much a string stretches when it strikes the ball. The more stretch, the more power it returns to the ball and the less impact it has on your arm and elbow. The less it stretches, the more energy is lost in flattening the ball and the less total power is available for rebound.
As in golf, the lower the dynamic stiffness 'score', the better. In the USRSA studies gut had a dynamic stiffness of 108 lb./in.
Nylon has been the most gut-like alternative to gut for many years, and has long been the gold standard for racquetball. Most current nylon strings are multifilaments: many thin strands of nylon, bundled in a protective jacket. Nylon strings are very inexpensive compared to other synthetics; are very responsive; not sensitive to moisture (or other chemicals, for that matter); and provide good abrasion resistance. In the USRSA studies, the dynamic stiffness ratings for several nylon string brands were approximately 190 lb./in. This is quite respectably low, especially when compared with aramid strings that top the stiffness scale at over 500 lb./in. Nylon's main drawback is that it loses tension more quickly than other string materials. This means it doesn't last as long in your racquet, so while it's less expensive, you have to buy more of it.
By comparison, the dynamic stiffness of Zyex came in at 145 lb./in, the closest to gut of any synthetic string material. It has even been called the "space age nylon." (In fact, Zyex is very much a space age material. (See our earlier column, "What in the World is Zyex, Anyway?"). This means it absorbs and returns impact force better than nylon. We call this "Soft Power" with our UltraKill® 17 and 18 gauge strings; "Ultra Power" with heavy-gauge UltraKill 16. Zyex controls the ball better than nylon, especially in thinner gauge strings, and holds tension much better than nylon, which means it stays playable in your racquet longer. Zyex is impervious to moisture and offers excellent abrasion resistance to enhance durability. And, it's very modestly priced.