Gear Talk: Solinco's KT Kim, Part Two

I recently sat down with KT Kim, a key director for string company Solinco. In part two of our conversation, we spoke about educating parents about polyester, how Solinco tweaks strings for touring pros, and the general process involved in manufacturing a polyester string. (For part one, click here.)

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Justin diFeliciantonio: You talked earlier about the trickle-down effect in tennis—i.e., how recreational players often want to use, say, the same polyester strings that their favorite pros are playing with. What’s your take on poly’s risk/reward profile for the rec. player?

KT Kim: Poly, in general, is something that I don’t think everyone should be using. Solinco is mostly known for our polyester strings. But we do have multifilament and synthetic strings. Actually, our multifilament Vanquish does quite well. But the question we get most often is, “Do you think my child should use polyester strings?” And although we want to sell a lot of our polyester string, our recommendation is always, “Don’t switch to poly until you actually have to.” Meaning, until your kids are able to break those multifilaments daily, or every two days, and it’s getting too expensive to keeping using those softer strings—this is an indication that they have the racquet-head speed, they’re strong enough, they’re hitting a big enough ball to actually even get the benefits of poly. So that’s when you start experimenting with a hybrid or thinner-gauge polyester strings at low tensions [JD: High 40s, low 50s, lbs.] The last thing we want to see are kids who aren’t able to play because of arm injuries. Which a stiffer poly can predispose you to. That’s a worse-case scenario.

JD: From what you’ve seen, what are some of the mistakes parents make when switching their kid’s string to polyester?

KK: If a kid is ready to use polyester, it’s important that he or she use it in the right way. Most of the time, kids will use multifilaments and string it in the high 50s, low 60s; that’s how I grew up, playing with those tensions. But when you go to poly, you shouldn’t be at those tensions. [JD: You should be 15 to 20 percent lower.] Parents should be aware that if they string up poly at that high tension, their kids are more likely to come down with injuries.

JD: Let’s talk about tour players using the string. You said earlier that Solinco doesn’t pay players to use the string. Who’s using Solinco on tour?

KK: That’s right, we don’t pay anyone to use our products. On tour, Donald Young uses our Tour Bite, as well as Igor Andreev, Malek Jaziri, and Evgeny Korolev. In fact, Korolev, since he’s had arm injuries in the past, he wanted something softer, so he uses our Outlast string. And we’ve actually done some string customization for [Nikolay] Davydenko.

JD: Oh really?

KK: Yeah. About a year ago, Davydenko was using our Tour Bite. But now that he’s gone to a racquet with a more open string pattern, we’re trying to tailor a string that will better fit his racquet and playing style. I can’t go into the details of it. But if players say I want x, y, and z, we actually work on it and try to manufacture it for them. I think a big part of it is, because we are a smaller company, we’re able to react quickly and on a personal level.

JD: So you don’t have to re-engineer the whole apparatus.

KK: No, no, no. We’re a very lean team, and can make things happen very quickly. But to give you a sense of the customization process: When we experiment and test out a string, we try not to test it out with guys that are on tour. We don’t want to involve them too early in the process. This is a psychological sport: If you throw too many things at someone, it becomes far too confusing. So once we have something we’re happy about, we’ll have ex-pros and other people try it out. And if they like it, we’ll consider custom making it for players, even if it’s not on the market.

JD: That’s fascinating. Speaking in general terms, how have you changed string for players? Like, diameter tweaks?

KK: Well, no. Construction tweaks. Composition.

JD: Of course, it’s easy to think of strings in terms of gauge or texture. But I’m always a bit skeptical of composition tweaks. Like, if a company says they add so-and-so resin to their string—it can be hard to determine whether that’s really changing how the string performs, or if it’s just marketing.

KK: I can’t speak on behalf of our competitors, but for us, we could make the same exact string with a different composition, and if you tried it out, it’d feel completely different. It really would. We’re always experimenting. Like with texture, for example. Before we’ve done the twisted, we’ve done the sharp edges. And right now we’re testing out some new constructions to see how they affect bite, how the string grips the ball.

JD: Now that we’re talking about the string itself, sell me on it. What makes Solinco a high-performance product?

KK: One reason is, just talking about the quality itself. When you actually manufacture polyester strings, there are two big variables you can tweak. One is the manufacturing process, and the other is the string’s composition. From both standpoints, we’re constantly experimenting in order to develop new products. That’s where we focus our money. I would say that since the last time we’ve released a string, we’ve tested over a hundred types of polyester strings. Like, literally.

JD: Really. So say you’re looking to create a new composition for a poly string: How do you go about it?

KK: Let’s say we’re trying to add a new chemical that will soften the polyester. When you’re actually doing that, one, you have to make sure that the compound actually improves the characteristics of the string. And obviously we do basic testing. We’ll add something, mix it around, manufacture it, then do elongation tests and measures of tensile strength, just to make sure the numbers make sense in the lab. But when you actually get it out there and play with it, does it feel good? That’s the most important thing, does it hold tension well, does it perform well? So if we’re adding one compound to our string, we might try, say, 10 variations of its quantity—put little bit, two times as much, three times as much, and so on. Test all these different variations out, in terms of how they hold their edges with tension (if the string has edges), as well as see if the string holds its tension and is durable.  

JD: So there’s chemical additives and composition tweaks that can affect how a poly plays. What about the second variable, the manufacturing process?

KK: Yes, there’s also the manufacturing. When you actually extrude the polyester, you’re heating it up and cooling it down, heating it up and cooling it down. There are several different stages of this. Even a string with the exact same properties, manufactured in a very different way, can produce a totally different string. It’s a pretty interesting process, and we try to think of new and innovative ways to change it up. The structure of how you manufacture is relatively simple. So within those bounds: How can you change things up a bit to make something new and interesting? That’s our challenge.