Materials used in String Construction

Gut

For many years racquet strings were made from natural gut – the intestines of sheep or cows – which provided the most effective balance of power and control. It has never been very durable and is particularly susceptible to moisture damage. Gut is a “natural multifilament” without a wrap or a braid, partially explaining its superior performance and lack of durability. The top range synthetic strings of today still aspire to the "pocket elesticity" of gut. It is expensive to manufacture and the frequent string replacement due to poor durability accentuate the expense placing it out of reach of most except the sponsored or rich.

Synthetic strings of today are still made to emulate the characteristics of natural gut. High speed video analyses show that gut strings have lower “dynamic stiffness” giving better “pocket elasticity” improving power and reducing loss of control, and better “dynamic elasticity” giving more power, than nylon strings of any construction. Some argue gut remains the ultimate string material while others believe modern technology has finally enabled equal or superior performance from the “synthetics”.
In summary gut gives excellent power, control and feel, wears very quickly, is expensive and remains the “overall performance” standard (excluding durability) to which the top synthetics still aspire.

Nylon
Nylon is a generic term covering many polymers. Advances in polymer technology have not only enabled tuning the suitability of these nylons and the way they are used to construct strings but also use of other materials which can significantly enhance string characteristics. The cores and wraps of most synthetic strings are still made from nylon, much of the advancement coming from the use of the multifilament construction with braided wraps . Generally speaking gains in power or control have come at the price of durability. Most “synthetic gut” is still nylon.

Polyester
Compared to nylon polyester is very strong with low elasticity. It is becoming more popular with tennis players prone to frequent string breakage but generates low power due to its low elasticity and can be the cause of shock induced injuries as it creates a stiffer string-bed cushioning little of the shock from the impact of the ball. The effectiveness of polyester can be enhanced by using it for the main strings in a hybrid string pattern with nylon crosses to add elasticity for power and shock absorption.

Kevlar
Kevlar is even stronger and stiffer than polyester making it very durable. All that is written above regarding polyester is further accentuated in Kevlar. It is usually only used for the mains in hybrid stringing configurations complimented by nylon for the crosses.

Zyex
A relatively new synthetic fibre used to construct strings specific to each of the racquet sports with properties close to those of natural gut. It is claimed to be closer in “dynamic stiffness” to gut than any other synthetic, to have extremely good resilience, be very strong and durable enabling use of narrower gauge strings for grip on the ball and holds its tension well even over extended periods. Ashaway use Zyex in their PowerNick and the new Ultimate string.