Polyester strings have revolutionized the world of tennis. Literally.

Their big spin potential allows players to put more revolutions on each ball. So it’s no surprise that the game of tennis has evolved so quickly since polys became mainstream in the early 2000s.

But the stiff, dead and controlled response has its downsides.

Not only do traditional polyesters lose out on the feel-factor of softer strings, they’ve also gained notoriety for being uncomfortable and are often linked to certain overuse injuries. Over the years, polyesters have developed, and the original, boardy strings have made way to softer, more playable and more comfortable offerings. These soft polys colour between the lines of their more traditional polyester cousins, and the softer multifilament, natural gut and synthetic gut strings.

The goal of a soft poly is to maintain the redeeming qualities of a polyester (spin, control and durability), while minimizing its negatives (discomfort and lack of feel). String brands are now devoting most of their resources to these new-age polyesters. A few stick out as being a cut above the rest. 

Luxilon Element

Luxilon are the king of polyesters. Their Big Banger Original and Alu Power are still some of the most popular strings on both the pro tour and recreational courts, 15 years after their release. But those strings are stiff. Luxilon Element maintains many of the core features in those strings, while drastically lowering the stiffness. Its “multi-mono” technology does exactly what its name suggests. It adds the feel and softness of a multifilament to the controlled and spin-friendly response of a polyester. 

It is important to note that unlike some of the other strings on this list, Element still very much acts like a polyester. It performs much closer to the likes of RPM Blast and Alu Power than it does to a synthetic gut, or a multifilament. Take those strings, add some comfort and a longer dwell time to the string bed, and you have the playability of Element. Of course, you’ll sacrifice a bit of that top end spin potential and control, but it’s a small price to pay for the right player. Also, like any polyester, Element will bag out, as well as lose tension and playability before the string actually breaks. Some soft polyesters perform much better in that regard.  

Luxilon Alu Power Vibe

One of those strings is Alu Power Vibe. Before I go on, I’d like to point out that Alu Power Vibe plays nothing like Alu Power. I’m not entirely sure why Luxilon has given it a similar name. Perhaps for marketing purposes? The two polyesters couldn’t be more different.

Alu Vibe is a string that brings the playability from a polyester much closer to that of a synthetic gut. Vibe could easily be mistaken for a multi or a syn gut, in a blind test. Yes, I realize a blind test is nearly impossible in a hand-eye coordination game like tennis. In terms of comfort, it is unlike any other polyester - well that’s not entirely true, but more on that later. I felt none of the vibrations and shock I usually feel when playing with polys. It also maintained its tension far better than other polys. Stringing up Vibe, I could feel the elasticity and stretch was much more similar to a synthetic gut, so that tension maintenance came as no surprise. 

What makes Alu Vibe so great is that it plays like a soft string but with the durability of a poly. After 6 hours of play I had barely notched through the main strings. With a multi, they would have broken already and with a synthetic gut, they would be nearly there.

That’s not to say Vibe is the perfect string. While it is groundbreaking in its playability and durability, the response off of the stringbed is very different to that of a traditional polyester. Its spin potential is mediocre and closer to that of a syn gut than a poly. Strung in a full bed, it also lacks that confidence inducing control of stiffer poly. For those of you who are used to stiff polyesters, this might just be too different. Trying this string in a hybrid would be a more interesting solution. You get similar durability to a full bed of poly, with the feel and comfort of a softer hybrid. For those of you who have played with multis and syn guts in the past, but are frustrated with their durability and would like a little more spin and control, Luxilon Alu Power Vibe is the perfect string. 

Babolat RPM Soft 

In my description of Alu Vibe, I used a lot of words indicating that the string was unique. And it would be, were it not for RPM Soft. Babolat and Luxilon are the two biggest string manufacturers in the world, so it comes as no surprise that both of their revolutionary, soft offerings came out within months of each other.

These two strings are incredibly similar, so I am not going to waste much time repeating my comparisons of Alu Vibe to stiffer polyesters. They both have best- in-class tension maintenance and comfort, and both lack spin potential and control compared to their stiffer counterparts. So what separates these two, one-of-a-kind polyesters?

RPM Soft is ever so slightly more powerful than Alu Vibe. I found it to have more of the trampoline effect of a multifilament, while also feeling softer for touch shots and comfort. It is also more spin friendly than Vibe. Stringing up the two, RPM Soft glided much smoother on itself, and that was consistent with my experience on court. There is more string snapback on RPM Soft, albeit still less than on traditional polys. It was also less durable than Alu Vibe. As it is a softer string, I notched through the mains a little bit quicker.

With that said, these two strings are incredibly similar and in their own category of soft polys, at least for the ones I have tried. RPM Soft is another string that should be tried in a hybrid. Durable but playable; yes please.  

Yonex Poly Tour Pro

Poly Tour Pro is the stiffest string on this list. That’s also why it's my personal favourite. It sacrifices the least amount of polyester playability, for a softer, more comfortable and more touch-oriented response. I feel like I can take a big cut of the ball, while staying confident my shot will land between the lines. Spin potential is also nearly as good as any of its stiffer competitors. One of my main gripes with soft strings (including the softest polyesters) is their inconsistent response to spin. Because the string is so soft, it tends to dig into itself, rather than glide seamlessly atop its surface when creating the snapback effect. When a soft string digs into itself, it leads to an unpredictable response off of the string-bed. Poly Tour Pro is just stiff enough to still provide that glide.

On the flip side, I have never found my arm to fatigue with Poly Tour Pro, the way it can sometimes with stiffer polys. I also love the response of the ball off of a full bed of Poly Tour Pro. Maybe I’ve grown used to the feel of polyesters, but there’s something about the short but noticeable dwell time that’s different to some stiffer polys. There is a clear snap and release that I don’t feel with every poly, and it's just the feedback I love from a slightly softer string.

The term “soft polyester” is still incredibly broad. On this list, you see strings that are close in playability to a multifilament, and others that are closer to those stiffer, more traditional offerings.

But that’s just what makes a soft poly so unique.

It is a string category that is significant because it accepts the importance of a polyester string design, while also understanding that those strings have drawbacks that must be addressed in order to open up the string category to the whole of the tennis industry. Each poly has its own unique playability, but soft polys are certainly the way of the future in string development for the majority.