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The Evolution of Poly Strings

A panel of string manufacturers helps sort through questions about poly, co-poly and who should play with them.

By Bob Patterson

There is no doubt poly strings are popular with everyone from top touring pros down to junior and recreational players. Along with that popularity, there seems to be an equal amount of confusion. What is the difference between “poly” and “co-poly”? What tension should I use? Is poly a good string choice for me?

The questions seem unending. So we set out to get some answers from the top manufacturers of poly strings.

What’s In a Name?

The confusion seems to start in the name. Originally called “polyester string” (yes, the same material your leisure suit was made from if you are as old as I am), they are now referred to as simply “poly” or “co-poly.” So what’s the difference?

The experts are fairly unanimous on this one. A “poly” string generally refers to a monofilament made from a single polymer called polyethaleneterephthalate (PET). Other polymers are also used such as PTT and PBT, according to Evan Specht, director of operations at Diadem Sports.

Tom Parry of Pacific relates the confusion of poly/co-poly to the similar confusion of what is “synthetic gut.” “Synthetic gut is simply a marketing term that became an accepted description of an advanced nylon string,” Parry says. “Essentially, both in their respective ways are derivatives of the same originating materials and compositions — nylons for synthetic guts and plastics for poly. We see higher grades of materials being used in both types, allowing for numerous differences in performance characteristics, as well as more complex manufacturing processes.”

“Co-poly” is generally referred to as this same string with other additives. Hunter Hines with Dunlop explains that additives are included in the mix to “bring about different physical properties (softer, more elastic, better tension maintenance, etc.)” than are found in the base poly.

Steve Crandall of Ashaway explains it this way: “Co-poly is a marketing term for poly strings with some additives in the polymer formation to modify the polyester’s negative properties.” Crandall also adds one tidbit that should not be overlooked. “No matter what additives are used,” he says, “the resulting string is much stiffer and less elastic than any other type of tennis string.”

What Are the Benefits?

So now that we know what it is, what are the primary benefits of this type of string to tennis players? Our panel generally agrees that durability and spin generation are the key components, although not all see it exactly alike.

Both Parry with Pacific and Josh Newton of Babolat point out a key ingredient needed for spin — player technique and skill. “You must already possess sufficient technique and racquet-head speed in order to get more spin from a poly or co-poly string,” Newton says.

Parry elaborates that the potential for spin is there, but a player will see the full benefit only when the “head speed and technique are there.” Parry provided the chart (opposite page) to illustrate the variations in the string and ball interaction with the various string types. As you can see in the illustration, “See how each type has its own bending curve, as well as how the ball energy is lessened as you go from gut to poly.”

Hines points out one often overlooked benefit: “The strings never seem to move, and rarely need adjusting, even at lower tensions. Of course, poly strings do move on impact, but are better at snapping back into place between shots.”

This snap-back seems to be the key ingredient to spin generation. Recent tests with high-speed video and tracking software shows that the snap-back generates the spin, but as our panel points out, it takes a lot of racquet speed at impact to move the stiffer strings in order for them to snap back and generate the spin players are looking for.

Durability is also misunderstood for most people. Yes the string is more durable in that it doesn’t break as quickly as other materials. However, the string does lose resiliency much faster than other materials, so if the player is not a frequent string-breaker, the durability is of no consequence. Newton points out, “Poly/co-poly strings lose tension incredibly fast, both statically (after stringing but before playing) and dynamically (while playing). Therefore they need to be replaced very frequently, or else you will lose control and power.” This could be the reason top touring pros go for a “fresh” racquet on every ball change (nine games).

John Elliott of YTex says poly/co-poly strings need to be restrung every two to eight hours of play depending on the density of the string pattern, the type of string and the gauge.

Who Should Use Poly/Co-Poly?

Are poly/co-poly strings suited for all player types and skill levels?

Most of our panel agree that poly/co-poly strings are best suited for skilled players who can generate the necessary racquet-head speed to flatten out the ball on impact. However, Specht says, “I think a well-made co-poly could be suited for anyone. I think if you have a soft co-poly that also increases spin, you have a win-win.”

Hines says, “If you are not a string-breaker and/or a spin player, I’m not sure you’d get much benefit out of poly/co-poly strings. The average recreational player would be wise to really weigh the options, as there are certainly drawbacks to poly/co-poly strings — especially for players who are prone to arm trouble or need more power and depth on their shots.”

Newton adds, “Most recreational players, including competitive juniors, do not possess the ability to get the spin benefits from poly/co-poly strings, and their games and often their bodies suffer from the down sides of poly — stiff, low power, poor tension holding.” He explains that to get the full snap-back effect to create spin, the player must first be able to move the stiffer string in order for it to snap back and only the top-level players have the ability to do so.

What’s Next?

So, what does the future hold for poly/co-poly string? Although most agree that poly/co-poly strings are best suited for a small segment of the market, they also think they are with us to stay. Most feel companies will continue to develop new constructions and additives to decrease the problems of quick tension loss and stiffness.

“My feeling is the drive is to make the strings more playable, powerful and have more spin potential, in an effort to make them more usable by a wider range of players,” Elliott says. “Unfortunately, poly/co-poly strings have limitations in these categories due to their molecular make-up.”

Hines adds, “There is a generation of younger players in the game who have only ever played with polyester or co-poly strings, so I think it’s more ingrained in the market than ever.”

Most agree that hybrids will be a big part of the advancement. “I think with today’s fast-paced, ‘knock the cover off the ball’ attitude and new stroke production being taught, poly is here to stay,” says Parry. “Hybrids are going to rule as players are realizing they can tweak more and more their performance using different strings.”

Several of our panel members say we will be seeing more hybrids in the future, including poly/poly hybrids.

Crandall says he thinks there is not a lot of room for technical developments of co-polys, but he sees “the future going to other polymers, filament designs, and physical structure.”

See all articles by Bob Patterson

About the Author

Bob Patterson , the founder of the RacquetMAXX customization service, is a Master Racquet Technician with more than 20 years of experience. He was RSI's Stringer of the Year in 2005. He is Executive Director for the U.S. Racquet Stringers Association.

From the May 2015 issue
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