A Short Course On String Design
By Steve Crandall
Vice President, Sales & Marketing
Ashaway Racket Strings
Badminton players who are familiar with other racquet sports like tennis and racquetball may be aware that there are hundreds of string models available, with dozens of different design features. The proliferation of choices, and confusing manufacturers' claims in these sports, is made possible by a wide array of composite string technologies, each relying on their own unique high-tech materials such as Vectran®, Kevlar® and Zyex®.
These composite technologies are not practical in badminton because the strings are much thinner. There is simply not enough diameter available to adequately bond another material to the string's core. A badminton string consists of three basic components-a core, a jacket, and an outer coating. With only three variables, it is not difficult to understand badminton string design choices and how they affect longevity and racquet performance.
The core is the central load-bearing member of the string. It provides strength and determines the majority of the string's "response" characteristics: how much it will stretch when strung in the racquet, how much more it stretches when hitting the ball, and how quickly it rebounds.
There are two basic core types: monofilament and multifilament. A monofilament core consists of a single thick nylon fiber. It may also be constructed of a few medium-gauge nylon fibers that have been chemically bonded together so they behave as a single thick filament.
Multifilament cores are made from thousands of very thin fibers twisted and/or braided together, but not chemically bonded. They're free to stretch somewhat independently from one another. As a result, multifilament cores are less stiff, or more resilient, than monofilament cores of the same material. This translates into sustained string performance and more gripping action for better shuttle control.
During a match, the main strings in the racquet move back and forth against the cross strings and would quickly be sawed through if it weren't for the string's abrasion-resistant jacket, also known as the cover or wear layer. The jacket also provides texture to the surface of the string, which is even more important than cross-sectional shape for "bite" or control. In multifilament strings, the jacket also holds the core filaments together.
Most monofilament jackets are twisted over the core, while multifilament jackets may be either twisted or braided. Twisting provides a smoother surface, making it easier to string the racquet. Braiding the multifilament jacket over the core produces a more textured surface than twisting does, for more bite.
When a fiber breaks in a twisted multifilament string jacket, it begins to unravel, and the string may deteriorate quickly with further use. With a monofilament string design, the twisted jacket is chemically bonded to the core and breakage occurs in a catastrophic manner, as a fiberglass fishing rod would fail when severely flexed repeatedly.
In a braided cover, the over-under-over design locks all the fibers together, so the breakage of a single fiber doesn't mean the imminent death of the string. In fact, many jacket fibers may break and the string will remain intact. The broken jacket fibers will stick out, producing a "hairy" surface that aids shuttle control. Eventually, of course, even braided jackets become so worn they can no longer protect the core.
Monofilament strings are usually coated with a phenolic resin which chemically bonds the monofilament core to the monofilament jacket, creating a single mass. This makes for a finished product with a smooth surface which is easy to string. However, the stiff unified structure is more likely to snap, so strings have to be replaced more frequently.
The multifilament design generally has a compatible "glue like" nylon resin coating which mechanically bonds all the different layers of multifilament fibers together. This provides a smooth finished surface for easy stringing. This configuration allows for a considerable amount of flex, and provides for longer life of the strings which wear one filament at a time.
When In Doubt-Play Test
With two types of cores and two types of jackets, there are four basic combinations of string construction. Beyond that, hundreds of other possibilities exist: core fibers may be twisted or braided, and may have different numbers and types of nylon fibers; jackets may be twisted or braided tighter or looser, and may consist of either one or two layers of different nylon polymers. The strands in each braid may be a single fiber, or may be a small bundle of two or three fibers.
Players need not concern themselves with this level of detail. However, the sensible approach is to identify the basic core and jacket designs that are appropriate to your style of play. Then, through play-testing, you can compare the string models that have the basic core/jacket combination you want and find the one that feels right for you.
Once you select the most appropriate string design, you should also hone in on the gauge of string that is best for you. When you are talking nuances of playability in badminton, that's when you need to get into the gauge issue.
This article previously appeared in Badminton News / USA.