Understanding Manufacturers' Claims - #1: The Materials
By Steve Crandall
Vice President, Sales & Marketing
Ashaway Racket Strings
Racquet strings differ from one another in three ways: gauge or thickness (which we've looked at in previous columns), materials, and construction. String manufacturers make all sorts of claims about the benefits of different high-tech fibers and proprietary manufacturing methods. We'll look at the materials in this installment, and consider string construction in a later issue.
The materials that go into racquetball strings-primarily aramids, Zyex(r), and nylons-are manufactured by large chemical companies. Racquet string manufacturers test and compare the different fibers that are available, and when they find one with desirable characteristics, they engineer it into a structure keyed toward a particular type of performance. Manufacturers often use more than one fiber type in a string design to combine their properties.
Aramid fibers get a lot of attention, so let's look at them first. Aramids, which include DuPont's well-known Kevlar(r) fiber, are also used in bulletproof vests, automobile tire cords, and top-end canoes. As you would expect, aramids are extremely stiff, tough, and resistant to stretching. In racquet string, Kevlar is used primarily for the core, or central load-bearing member. (Example: Ashaway DuraKill(tm)) At recommended stringing tensions of 25-55 lb., Kevlar stretches only about 3 percent.
Because of their stiffness and lack of stretch, Kevlar-cored strings don't have much "trampoline effect"-in other words, they don't provide a lot of power. A Kevlar string bed remains flat during hard killshots, so players can maintain a superior level of control.
Aramids are also extremely notch-resistant, and have extraordinary tensile strength
(i.e., resistance to breakage due to stretching), so they tend to be very durable. There are a few strings that use Kevlar not just for the core, but for the cover layer as well. These are so stiff that they are used almost exclusively as the mains in hybrid string sets, while a second, softer string is used for the crosses. (Example: Ashaway KillFire(tm)).
In sum, aramid strings are for powerful players who want improved ball control, and for those who want extra string longevity. If you don't have a really strong swing, keep reading.
Zyex(r), the other well-known high-tech fiber, is a poly ether ether ketone (PEEK) material
introduced by British chemical giant ICI, and recently spun off as Zyex Ltd. More flexible and resilient than Kevlar, Zyex is still pretty stiff compared to nylon: at typical stringing tensions it stretches about 6 percent.
Zyex's remarkable characteristic is its "dynamic stiffness,"-that is, it recovers from stretch very quickly. A racquet strung with a Zyex-cored string maintains a fairly flat string bed,
which helps in ball control, but the rapid recovery from stretch provides good power. Tennis players believe that Zyex performs similarly to natural gut, which is still the string of choice for many top-ranked tennis pros. But Zyex is far more durable than gut, making it a fine material for racquetball strings. (Example: Ashaway PowerKill(tm) Pro) For players looking for a good balance of power and control, Zyex is an excellent choice.
Nylon is a do-anything material, with different chemical compounds appearing in everything from women's stockings to machine bearings. String designers use nylon's broad range of properties for different purposes. When used as a string core, nylon provides a great deal of resilience. Although it doesn't spring back as quickly as Zyex, it stretches more, so the amount of power it generates can be comparable. In fact, nylon can be quite stretchy or quite stiff, depending on the gauge of the string. At typical stringing tensions, nylon stretches from 10 to 15 percent. Nylon-cored strings tend to be the least expensive on initial purchase, and tend to be easier to string than those made from stiffer fibers. (Example: Ashaway SuperKill(r) II) Nylon strings are great for beginning players, for those who can afford to give up a little control in order to gain power, and for anyone who needs to keep an eye on the contents of their wallet.
Nylon also appears as the outer jacket, or wear layer, on most strings, including those with Kevlar or Zyex cores. For this usage, string designers often choose a harder, less resilient nylon fiber, to resist wear and notching, and to bond the core fibers together.
The different fibers in racquet strings influence their power, control, durability, and cost. Whether you're working with a Certified Racquet Technician, or buying through a mail-order ad, you can get the properties you want by selecting a string made from the right materials.
This article previously appeared in Racquetball Magazine.