Tennis Industry magazine


String Playtest: Ytex Square-X

By Greg Raven

Ytex Square-X is a square profile monofilament string containing co-polymer, carbon and polyolefin that is finished using a Thermo Foil Cooling Process. Ytex claims that where the mains and crosses contact, the two flat surfaces increase durability, eliminate notching and allow the string to return to the “neutral” position after impact with the ball.

Ytex tells us that because Square-X measures 1.20 mm across the flat sides, it plays like a much thinner string, increasing power and control.

Ytex Square-X is designed for players who love poly and co-poly but are looking for a softer string that is easy on the arm.

Square-X is available in 16L (1.25 mm) in black or white. It is priced from $5.50 for 40-foot sets (retail $8.50), and $64 for reels of 660-foot (retail $99). For more information or to order, contact Ytex at 843-816-1440, or visit

In the Lab

We tested the 16L-gauge Square-X Black. The coil measured 40 feet, 8 inches. The diameter measured 1.24 mm prior to stringing and 1.22 mm after stringing. We recorded a string-bed stiffness of 77 RDC units immediately after stringing at 60 pounds in a Wilson Pro Staff 6.1 95 racquet (16 x 18 pattern) on a constant-pull machine.

After 24 hours (no playing), string-bed stiffness measured 73 RDC units, representing a 5 percent tension loss. Our control string, Prince Synthetic Gut Original Gold 16, measured 78 RDC units immediately after stringing and 71 RDC units after 24 hours, representing a 9 percent tension loss. In lab testing, Prince Synthetic Gut Original had a stiffness of 217 and a tension loss of 11.67 pounds, while Ytex Square-X Black 16L has a stiffness of 214 and a tension loss of 12.46 pounds. Square-X Black 16L added 16.1 grams to the weight of our unstrung frame.

The string was tested for five weeks by 27 USRSA playtesters, with NTRP ratings from 3.5 to 6.0. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. The average number of hours playtested was 29.8.

Ytex supplied us with a tension chart for specific head sizes and mains counts, with a general recommendation to set the reference tension 5 percent to 10 percent lower than for a typical nylon string. We passed these recommendations along to our playtest team.

Ytex Square-X has rounded corners, so installing it was not a problem. We saw some burning, although only one playtester reported this.

No playtester broke the sample during stringing. Three reported problems with coil memory, one reported problems tying knots and one reported other problems.

On the Court

Our playtesters loved the Spin Potential of Square-X, rating it 20th best in this category of the 194 strings we have playtested for publication. Ytex Square-X also rated well above average in Durability, Resistance to Movement and Control. Overall, Ytex Square-X rated above average.

No playtester reported premature fraying or peeling, none reported buzzing and four reported notching. Only one playtester broke the sample during the playtest period, after nine hours of play.


If this reminds you of an “untwisted” version of the Ytex Quadro Twist we playtested for the February 2012 issue of Tennis Industry magazine, you are in the right ballpark. One difference is that our playtesters rated Square-X to have even more Spin Potential than Quadro Twist.

Playtester Comments

“I liked the spin of the string and the ball pocketing. I thought it played well, and played better after a few hours. Easy access to spin reminded me of RPM Blast.” 5.0 male baseliner with heavy spin using Babolat Pure Storm Limited strung at 53/51 pounds LO (Forten Thin/Forten Synthetic 18/17)

“This string has good feel and durability. Most shots feel comfortable, and serves and overheads sure do feel solid. This string seems durable, and feels great on touch shots like drop shots and drop volleys. All around a good string.” 4.0 male all-court player using Prince TT Viper strung at 54 pounds LO (Gamma Ruff 16)

“It was a very responsive string right out of the box. Provided good feel and power without any break in period and it held its tension and playability through the test. I would recommend this string to anyone. I don’t think it needed the additional stringing guidance, the simple 5-10% less tension would suffice for experienced stringers. As stated, I would recommend this string for any level of play. It’s not as rigid as some polys and it does not lose tension like others.” 4.0 male all-court player using Prince Red LS 105 strung at 55 pounds LO (Gamma TNT2 17)

“This string was enjoyable to play with. It had a nice combination of the three essentials needed in every string: Comfort, control, and power, with the strongest leaning toward control. It maintained tension well and resisted movement. Good string for everyone.” 4.5 male serve-and-volley player using Prince Tour 100T ESP strung at 48/52 pounds LO (Prince Tour XP 17)

“Overall, very impressed with this string. Great spin, and the durability was surprisingly good! The playability was very good as was the feel. I was pleasantly surprised with the overall performance of this string. It felt like it would be stiff during installation, but played ‘softer.’ Would use this string for sure!” 6.0 male using Wilson Juice 100S strung at 55 pounds CP (Luxilon 4G 17)

“Liked the string. Seemed to keep its tension and playability. I enjoyed the amount of spin I could get on my serve and volleys. Provided plenty of spin and control on groundstrokes and approach shots. Did not feel it lost its liveliness during the hours of use. Would use in a hybrid situation as well as by itself. No issues on arm. Enjoyed hitting this string.” 5.0 male all-court player using Prince Tour 100 ESP strung at 48 pounds CP (Prince Tour XC 16)

“I like this string. It has a little bit of texture to it that my normal string doesn’t. That was a big plus. Would like to see other color than black.” 4.5 male all-court player using Prince Warrior 100L strung at 52 pounds LO (Prince Warrior Poly)

“Overall a great string that proved to be near the top for all qualities evaluated except it seemed to have less power than my normal strings. Stringing was easier compared to strings of similar construction. The strings felt and played great from the initial hit — there was no time period in which I had to become accustomed to a new string. Although stiff, they did not play like a ‘stiff’ string — feel, touch, and comfort were each excellent. The best qualities of the string overall were its durability, resistance to movement, and ability to hold tension. Highly recommended!” 4.5 male all-court player using Prince O3 Red strung at 53 pounds LO (Tecnifibre X-One Biphase/Tecnifibre NRG2 18/18)

“Liked the ease of stringing for the kind of string. It held tension well. Would use it when it hits the market.” 4.0 male all-court player using Wilson Burn 100S strung at 55 pounds CP (Wilson Revolve 17)

“Felt good for a poly. Seemed to bite quite well with good serve performance.” 5.0 all-court player using Prince Warrior strung at 55 pounds CP (Prince Premier Power 17)

“Good-looking, black string. Easy and fun to play with, but underpowered for the type of frame I used that particular week. I would like to try it in a Pure Drive or Pure Aero.” 4.5 male touch player using Angell TC 95 Custom strung at 55/52 pounds CP (Babolat VS/Babolat RPM Blast 17/18)

“We always pre-stretch string for 15 minutes at room temperature to decrease the tension loss. The string played surprisingly well for what we thought was an all-polyester string.” 3.5 male all-court player using Wilson 2.0 Hyper Hammer strung at 50/45 pounds CP (Gamma Poly Extra/Gosen OG Sheep 18/17)

“Does what a poly does with added spin and durability. Comfort and touch are second to spin and durability.” 5.0 male serve-and-volley player using Wilson Pro Staff RF strung at 48 pounds LO (Gamma Live Wire Pro 17)

“Two things that stood out with this string are: 1) It held tension better than any string I’ve tested in recent memory, and 2) It had remarkable control given the ‘low’ stringing tension used. I expected to have a string bed that resembled more of a trampoline feel and not the smooth controlled feel and moderate power I actually experienced while hitting. Overall, I liked this string although I would like better spin production.” 4.0 male baseliner with heavy spin using Volkl Organix 8 Super G 300g strung at 50 pounds LO (Luxilon Savage/Solinco Tour Bite 16/17)

“Good string for people who want spin and control.” 4.5 male all-court player using Babolat Pure Aero strung at 50 pounds CP (Babolat Origin 17)

“Overall, for a poly it was average. Played well, and easy on the arm. Wish it had more pop. I should have strung it 5 to 10% less.” 5.0 male all-court player using Head Prestige Graphene strung at 60 pounds LO (Head Sonic Pro 16)

“Average string; not something I would buy.” 5.0 male all-court player using Head Prestige strung at 50/46 pounds LO (Tecnifibre NRG2 16)

“Good overall string. Not enough power for my game though.” 3.5 male baseliner with heavy spin using Wilson BLX Blade 98 strung at 55 pounds LO (Gamma Professional 17)

“Took awhile to get used to as I use 17 gauge in mains and spin in crosses. Found the ball to fly more in the beginning, but was able to adapt quickly. Control was more of an issue all the way to the end of testing.” 4.0 male using Wilson Pro Staff RF strung at 59/56 pounds CP (Wilson Synthetic Gut Duramax/Luxilon 127 Spin 17/16L)

“Started out OK and then began to fade really fast (at about the 20 hour mark).” 4.0 male all-court player using Prince Warrior 107 Textreme strung at 50 pounds CP (Prince Tour XP 17)

“As recommended, I dropped the tension from my normal 57 pounds to 49 pounds, and was not able to control my shots with any regularity. When using this string, I would not recommended dropping the tension more than five pounds from your normal tension.” 4.0 male baseliner with moderate spin using Pacific Raptor strung at 49 pounds CP (Pacific Premium Power X 16)

“For the first few hours this was a great string. It had all you want from a poly: Some comfort and feel with a lot of spin and control. However, the string aged poorly and after about five hours turned into an average poly that was harsh and didn’t produce that much spin. For people who can afford to string frequently, this would be a good choice, considering how well it played for the first hours. Players looking to hit for an extended time with the same string job should look elsewhere. I’m curious to try this string in a hybrid setup and see how that works out.” 4.5 male all-court player using Wilson Pro Staff 90 strung at 50 pounds CP (Volkl Classic Synthetic/Topspin Cyber Blue 16/17)

“Was not accustomed to the really low tension requested. It took a little getting used to. Did not find any particular advantage with the lower tension, but felt it might have given more power, rather more depth through the trampoline effect. I would assume more spin as well, but not measurable.” 5.0 male serve-and-volley player using Wilson Juice 100S strung at 46 pounds CP (Luxilon 4G/Wilson NXT 16L/16)

“The first couple of minutes hitting, the string felt stiff, especially on off center hits. But as I continued to play, I got used to that feeling. Because of the lack of texture on the string, ‘feel’ shots lost some control. But, I was able to swing away from the baseline. Volleys got a good ‘pop’ from the string. The string felt softer than other monofilament strings that I have play tested.” 4.0 male all-court player using Volkl Organix 4 Super G strung at 53 pounds CP (Volkl V-Twist 17)

“I did not like the string at all at the beginning, but liked them better as the string broke in. I felt a slight discomfort in my elbow at the very beginning, but that went away as the string broke in after about five hours of play. I would try the string again in a hybrid setup. It was a good string but not a great string. There was no wow factor for me.” 4.0 male all-court player using Volkl Organix 10 Super G 295g strung at 48 pounds CP (Volkl Cyclone/Tourna Synthetic Gut Armor 19/17)

“Having to lower the tension with this string felt like I lost some of the feel but gained a lot more pop than normal. Stiffer sweet spot didn’t give me much feel with touch shots.” 4.5 male serve-and-volley player using Wilson BLX Two strung at 56 pounds LO (Luxilon 4G/Wilson NXT 16/16)

“Even stringing at a lower tension the string was very hard and had very little touch. I feel had I strung it a lot lower this would have been better all the way around. The stringing instructions that were sent need to be adjusted lower. The strings started to hurt my arm toward the end of the testing time.” 4.0 male serve-and-volley player using Prince Warrior Textreme strung at 45/47 pounds LO (Prince Tour XT/Prince Premier Touch 18/16)

(Strings normally used by testers are in parentheses. For the rest of the tester comments, visit

Playtester Ratings:

Ease of Stringing (compared to other strings)

Much easier: 1
Somewhat easier: 3
About as easy: 17
Not quite as easy: 4
Not nearly as easy: 0

Overall Playability (compared to the string played most often)

Much better: 1
Somewhat better: 5
About as playable: 6
Not quite as playable: 13
Not nearly as playable: 1

Overall Durability (compared to other strings of similar gauge)

Much better: 5
Somewhat better: 8
About as durable: 13
Not quite as durable: 1
Not nearly as durable: 0

Rating Averages From 1 to 5 (best)

Playability: 3.2
Durability: 4.0
Power: 3.1
Control: 3.6
Comfort: 3.1
Touch/Feel: 3.0
Spin Potential: 3.7 (20th overall)
Holding Tension: 3.3
Resistance to Movement: 3.7

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About the Author

Greg Raven  is an associate editor for Tennis Industry magazine and technical writer. He is certified as a Master Racquet Technician by the U.S. Racquet Stringers Association. He can be reached via e-mail at, or through Facebook, LinkedIn, and Twitter. He plays tennis three to five days a week, and is turning into an avid cyclist.



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