Ashaway’s ‘man-made natural gut’

September 12, 2012

Ashaway, RI — In a recent column on his company’s website, Ashaway Vice President and frequent stringing commentator Steve Crandall says that newly developed tennis strings made from a polymer material called Polyketone, or PEEK, play more like natural gut than any other synthetic string yet devised. According to Crandall, the key to the gut-like playability of these strings, which are marketed under the brand names Dynamite® and MonoGut® ZX, is their “dynamic stiffness.”

“What makes gut a superstar,” says Crandall, “is its ability to stretch on impact and then rebound quickly without deformation or loss of tension. This quality is called “dynamic stiffness” and 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 you “pocket” the ball and enhances control; 4) gut maintains tension over the life of the string, enhancing its value.”

On the downside, Crandall added, gut is very expensive and, without protective coatings, is very sensitive to moisture—it sags.

Crandall says dynamic stiffness can be likened to elasticity. He quotes Bruce McIntosh, the inventor of the leading PEEK string material, Zyex®, who defines dynamic stiffness as “the ability of a material to resist stiffening up as it is rapidly stretched and released—become ‘boardy.’” It’s measured in pounds per inch, and in layman’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.

Dynamic stiffness is measured in pounds per inch, and as in golf, the lower the rating score, the better. Using data supplied by the US Racquet Stringers Association, Crandall shows that Zyex-based Dynamite and MonoGut ZX strings have dynamic stiffness ratings of 145 and 151, respectively, compared to 102 for the top selling natural gut. In contrast, the leading polyester and copolymer strings are much stiffer, with dynamic stiffness ratings generally in the range of 220 and 250 lbs./in.

Says Crandall, “By comparison, the dynamic stiffness of Zyex is the closest to gut of any synthetic string material. That’s why we call it a “manmade polymer equivalent to natural gut.” This means it absorbs and returns impact force more like gut. It controls the ball more like gut, especially in thinner gauge strings, and holds tension as well as, or perhaps even a bit better than gut. Zyex is impervious to moisture and offers excellent abrasion resistance to enhance durability. And, of course, it’s cheaper than either gut or the high-end polyesters.”

All of Steve Crandall’s tennis stringing tips columns, including, “Ashaway’s Zyex®-Based Tennis Strings: the New ‘Manmade Natural Gut,’” can be found at

Ashaway Racket Strings are made by Ashaway Line & Twine Mfg. Co., the only U.S. manufacturer of string for squash, tennis, racquetball, and badminton. Operated by the Crandall family since 1824, Ashaway has been making racquet strings since 1949, and is responsible for several important technical innovations. Ashaway is the Official String of USA Racquetball and the Women’s International Squash Players Association. Ashaway Line & Twine Mfg. Co. also makes braided products for medical and industrial applications. For more information visit

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