What Are Co-Polyester Tennis Strings?

Co-polyester tennis strings like Zero, Sync, and Vivo are monofilament strings made from a polyester base blended with performance additives like resins, polymers, and plasticizers.

These additives are what make them "co" polyester strings, meaning they are a combination of polyester and other materials engineered to enhance how the string plays.

They represent an evolution from traditional polyester strings, designed to improve performance, tension maintenance, and comfort beyond what a basic polyester formulation can offer.

It’s worth knowing that most modern polyester strings on the market today are technically co-polyester strings with some combination of performance additives in their formulation, even if they are simply marketed as "polyester."

In this article, you will learn how co-polyester strings compare to traditional polyester strings, the best co-polyester string options in 2026, and how to use co-polyester strings in your setup.

Co-Polyester vs Polyester Strings

The differences between co-polyester and polyester strings come down to how the additives in co-polyester formulations change the playing experience.

Factor	Polyester	Co-Polyester
Comfort	Very stiff, harsh on arm	Softer, more arm-friendly
Tension	Loses tension rapidly	Better tension maintenance
Playability	Goes "dead" quickly	Maintains fresh feel longer
Elasticity	Stiff and rigid	Improved through additives
Feel	Muted and board-like	More responsive
Spin	Excellent	Excellent
Control	High	High

Traditional polyester strings are stiff and harsh on the arm, while co-polyester strings use additives to soften the response and make them more arm-friendly.

Where traditional polyester strings lose tension rapidly and go "dead" quickly, co-polyester strings retain tension significantly better and maintain a fresh feel longer.

The elasticity is also improved through the additives, giving co-polyester strings a more responsive feel compared to the rigid, muted, board-like sensation of traditional polyester.

Where both string types perform similarly is in spin and control, which is characteristic of the polyester material itself compared to other softer types of tennis strings.

Best Co-Polyester Strings from ReString

Zero

Zero is our flagship co-polyester string built for power and spin. Its hexagonal profile delivers maximum bite on the ball and unparalleled snapback, giving you aggressive grip on every groundstroke.

The string features our ultra-slippery Signature Snapback coating, which enhances string movement by reducing friction between the mains and crosses. This gives players superior spin potential as the strings slide and snap back into place quickly after contact.

Zero is the ideal string for power and spin players seeking aggressive, explosive groundstrokes. If you want to dictate the point with heavy topspin and big cuts, this is the string for you.

It is also engineered for superior tension maintenance, meaning the fresh, lively feel you get on day one lasts significantly longer than most co-polyester strings on the market.

Sync

Sync takes a different approach. Its round profile is designed for excellent control and precision, giving you a stable and predictable launch window on every shot.

The amplified feel of the stringbed provides a deep connection and feedback on every shot, almost like an extension of your arm. You feel exactly where the ball is going before it leaves the strings.

Sync is the ideal string for precision-oriented players who build tactical patterns and want to hit to small windows consistently. If you win points through placement and depth management, Sync was designed for your game.

It also features the same Signature Snapback coating technology as Zero, meaning you still get strong spin potential alongside the control-first response.

Vivo

Vivo brings a shaped profile that provides exceptional ball bite and control. Its crisp, direct response rewards good technique and full swings with precise feedback at impact.

What sets Vivo apart is that it is made from recycled polyester, delivering sustainable performance without compromise. You get real, competitive-level performance from a string that is better for the planet.

Vivo balances control with spin through its shaped profile. The shaped edges grip the ball for dipping spin and sharper angles, while the firm feel keeps your shots composed and predictable.

It represents the first string on the market that combines sustainability with high-performance characteristics, proving that environmentally conscious choices do not have to mean sacrificing your game.

How to Use Co-Polyester Strings

Tension Guidelines

A general guideline for co-polyester strings is to string 5-10% lower tension than you would with natural gut, multifilament, or synthetic gut.

Co-polyester strings are inherently stiffer than softer string types, and that stiffness requires lower tension to get optimal feel and performance. Stringing too high can make the response feel harsh on the arm, which defeats the purpose of choosing a co-polyester over a basic polyester.

For all ReString co-polyester strings, we specifically recommend stringing 2 lbs lower than your usual poly setup. This helps maximize the snapback that our strings are engineered to deliver.

Ideal Player Profile

Co-polyester strings suit intermediate to advanced players with fast, full swings. These players generate their own pace and benefit from the control and spin that co-polyester provides.

Players who are still developing their strokes or who rely on the string to generate power for them may find co-polyester strings less forgiving.

Co-polyester does not offer as much easy power as a softer string like synthetic gut or multifilament, and the stiffer response can be tougher on the arm for players who do not swing through the ball aggressively.

Hybrid Setup Options

Many players combine co-polyester in a hybrid setup with another co-polyester or a softer string to customize their setup and get the best of both worlds.

ReString's most popular hybrid setup is Zero and Sync, which pairs Zero's power and snapback in the mains with Sync's control and pocketing in the crosses. This is also the setup used by ReString athlete and WTA pro Cristina Bucsa.

Conclusion

Co-polyester strings are the modern, high-performance standard in tennis strings, improving on first-generation polyester strings with better comfort, tension maintenance, and feel.

They are designed for intermediate to advanced players who generate their own power and want a string that rewards their technique with spin, control, and durability.

Experiment with tension and string selection to find your optimal setup. Try Zero for power and spin, Sync for control and feel, or Vivo for spin, control and sustainability.

About the Author: Juan is the co-founder of ReString. He was born in Argentina, raised in Japan, and moved to the US to pursue college tennis. He now plays as an ATP & WTA hitting partner.