How Polyester Strings Generate More Spin on the Tennis Ball

Apart from mastering tennis gameplay itself, there’s a multitude of gear and equipment available to help players reach their full potential. In addition to the many possible racket customizations, string material is an essential factor that can affect gameplay, especially spin, as experts and players alike have found.

Just like the process of settling upon the right racket weight, length, or string tension, picking the right material for your stringing ultimately comes down to your style of play and level of experience. If you play consistently, you’re likely to notice when the response of each hit feels different than usual. Experienced players are sensitive to slight changes in feel, which often can be due to the choice of material and how it factors into the way they play.

Durability and spin generation are the key upsides to polyester stringing generally, although not all see it exactly alike. A key ingredient needed to leverage spin is player technique and skill. Generally, it’s necessary to possess proper technique and racquet-head speed in order to get more spin from a polyester string.

How Polyester Strings Generate More Spin

In 2011, the University of Sydney’s Physics Department conducted an in-depth study on the effect of different stringing materials on the spin of a tennis ball. In this exhaustive study, the experimenters Rod Cross and Crawford Lindsley painstakingly tested the differences between over 16 different tennis strings, using both clamped and hand-held rackets.

Tennis players for many years have claimed that there are noticeable differences between tennis strings in terms of the amount of spin they are able to generate. It’s true, of course, that players can deliver spin via specific strokes or angles of attack. However, the consideration for this study examined the effect on spin of different materials; all else held equal.

In a nutshell, Cross and Lindsley’s main finding was that polyester strings generate significantly more spin than nylon strings. This finding matched a 2006 study by the ITF (International Tennis Federation). They carried out tests on several different strings, also finding that polyester strings tend to generate slightly more spin than nylon strings.

Cross and Lindsley’s study was significant in that it supported previously articulated findings by the ITF as well as matched common accounts from players themselves. They indicated that polyester strings generate more spin than nylon strings. Also, in spite of the ITF study, there was not much literature present studying spin.

However, that still doesn’t quite answer the question: what about polyester actually causes the increased spin? In short–friction. What they found was that there were two main ways in which friction interacted with the incoming ball.

  1. The texture of the polyester string itself was such that it could exert more friction on the ball. That is, the polyester string gripped the fuzzy surface of the ball better than the nylon and other materials.
  2. They looked at high-speed photographs and videos of incoming balls and identified how much the strings themselves move as a result of contact with the ball. They called this “string movement.”

Think about when you push firmly to the side against one of your racket strings. There’s a little bit of travel; then, it goes back to its position in the middle of the two adjacent strings. This also happens at very high speeds during gameplay. Most of the time, when the racket makes contact with the ball, we can’t see it because it happens so fast.

So, not only is the friction against the ball itself having an effect, but the bungee-like effect of the “string movement” or “snapback” against the ball also affects spin. The two experimenters here determined that the friction of the strings against each other would determine the level of string movement.

They tested this idea by orienting two lengths of the same type of string perpendicularly, creating a contact point at the cross. They then dragged one length of string along the other and subjectively examined how much friction seemed to be present.

One of the more interesting points of the study mentioned above was that one of the natural gut strings exceeded one of the polyesters.

Looking at some of the gut options, it’s clear that they hold up at the same level as many of the polyesters. A few further observations:

  • The average polyester spin compared to the ordinary nylon is +20.2%.
  • The difference in spin between the highest and lowest poly is +15.9%.
  • The difference in spin between the highest and lowest nylon is +26.8%.
  • The difference in spin between the highest string and the lowest string is +49.3%.

Other Upsides of Polyester

Polyester is one of the most widely used materials for tennis racket stringing, and for good reason. It’s reasonably durable, affordable, and can be tensioned at different levels, depending on player preference.

Polyester stringing, while subject to normal wear and tear during play, tends to hold tension reasonably well. It’s worth noting that, due to the tension present in the strings, elasticity and tension begin to diminish the moment they are installed in a racquet.

“Dead strings,” or strings which have lost their tension, cut down on the performance of a racquet. Dead strings may also hamper a tennis player’s ability to generate power and pace, and may even make their arm sore. High-quality and properly-installed polyester stringing can minimize the emergence of dead strings and the effect of wear and tear on functionality.

Final Thoughts

In the last few years, more studies have been conducted, and certain types of polyester have continued to gain reputations for being conducive to better spin. Furthermore, Crawford and Lindsley contended that these recent findings found:

  • String texture or shape makes no difference to spin
  • String pattern makes no difference to spin
  • String tension makes no difference to spin
  • String gauge makes no difference to spin
  • String material makes no difference to spin

It’s unclear how definitive any of these conclusions can be notwithstanding further research. However, research seemed to be firm on the fact that variations in spin were far more significantly affected by differences in “incoming parameters” rather than racket or string characteristics. That is, the effects of slight differences in, say, the texture of a polyester string are minuscule when compared to other “incoming parameters,” such as ball speed, stroke power, angle of attack, grip style, etc.

Despite the challenges of disentangling these complex variables, researchers, according, at least, to the Crawford and Lindsley study, also noted another complication: the stiffness of different materials.

They noted that because of the increased stiffness, polyester deforms the ball more, relative to other materials–resulting in less power from the same swing. Because of this, players with polyester rackets tend to swing faster on average, because they are compensating for this inherent loss of momentum–and what happens when players swing faster at an angle? Higher spin.

In other words, “polyester’s stiffness caused less power that in turn allowed players to swing in ways that produced more spin and speed…that is, it wasn’t that the string was more ‘spinny’, but that it behaved in ways to [encourage] the player to perform more spin-friendly strokes” (Tennis Warehouse, Crawford and Lindsley 2011).

At any rate, researchers are still fully understanding the interactions between these variables while taking into account the subjective experiences of players.

Crawford and Lindsley encourage readers and players to put their findings in perspective. The difference in a total change in spin compared to the highest spin changer was about 1 to 5% for the polyesters, 5-12% for the nylons, and 3-5% for the gut. The difference in strings depends on how you look at the data and what your goal for understanding it is.

From one point of view–the player’s perspective, we’re concerned about both applying spin and battling incoming spin. So to think about how these seemingly subtle differences affect gameplay from a high level. It can be easy to get caught up in the nuts and bolts, the stroke-by-stroke of measuring spin, and what it all means for both consumers, players, and spectators. Tennis is a sport that takes place fast and in real-time.

The reality is, it’s hard to gauge until you spend some time experimenting with your own personal preferences and playing style.

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