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Tecnifibre X-One Biphase String Review & Playtest

Everything You Need to Know

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By Jon Crim

X-One Biphase is a premium multifilament string that combines the best of Tecnifibre’s technologies into a single string to produce power, comfort, and gut-like feel.

One of the string’s standout qualities was comfort. Even strung at a higher tension, X-One Biphase still retains its cloud-like comfort, which is ideal for players suffering from tennis elbow or simply looking for an all-around arm-friendly string.

However, X-One Biphase’s star quality was its raw power, which is at the top of its class. The ball jumps off the strings, making for a really fun playtest, especially when I had the opportunity to crank a few winners.

Combine the string’s comfort level with its power, and it makes for a unique combination where the string is naturally comfortable on your arm, and you don’t have to work too hard or strain your arm to generate pace.

While the string’s slick coating contributes to its power and comfort level, it did leave us longing for a bit more grip. However, after about 30 minutes of playtime and a little extra focus on generating topspin, I began to find my rhythm.

X-One Biphase is an all-around terrific multifilament string that’s great for players looking for extra comfort and some extra pop.

Article Contents

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X-One Biphase Specifications & Rating

Manufacturer Tecnifibre
Name X-One Biphase
String Type Multifilament
Technologies PU 400 – Elastyl – Biphase
Available Colors Natural white and red
Available Gauge 16/1.30mm – 17/1.24mm – 18/1.18mm
String Length Set: 40 feet (12m) Reel: 660 feet (200m)
Cost $$$ – Get it On Amazon
Durability 7.5
Comfort 8.7
Power 9.2
Control 7.5
Touch 8.6
Spin 6.8
Tension Stability 8.8
String Movement 8.7
Overall 8.2

Where to Buy X-One Biphase

Store Price
Amazon $$$
DoItTennis $$$
TennisWarehouse $$$
TennisExpress $$$

About Tecnifibre X-One Biphase

Tecnifibre’s X-One Biphase is a premium multifilament string built with three key goals in mind: power, feel, and comfort.

X-One Biphase comes in three different gauges: 16/1.30mm, 17/1.24mm, and 18/1.18mm. You can also pick it up in natural white or red, which is pretty cool.

Key features for X-One Biphase include:

  • PU 400: X-One Biphase is infused with a proprietary polyurethane that delivers 400 percent greater elasticity, therefore increasing the power potential of the string while reducing vibrations and increasing the overall comfort or decreasing impact to your arm with a natural gut-like feel.
  • 50 percent Elastyl, 50 percent H2C fiber: X-One Biphase is constructed from thousands of individual fibers with a makeup of 50 percent Elastyl and 50 percent high heat capacity (H2C). Elastyl is Tecnifibre’s trademark polyamide or nylon, which are incredibly soft fibers that deliver 12 percent more power than standard nylon strings. H2C fibers, on the other hand, are manufactured and bonded using a high-temperature pre-stretching step intended to provide superior tension maintenance.
  • Biphase process: Tecnifibre uses its patented two-phase process to produce the string, which increases the durability and life of the X-One Biphase by 20 percent.

All in all, Tecnifibre’s X-One Biphase packs a technological punch to bring players of all levels a top-notch multifilament string that many will find to be one of the best synthetic alternatives to natural gut.

A photograph of Tecnifibre X-One Biphase string on a slate table.

A zoomed in photograph of Tecnifibre X-One Biphase string on a slate table.


When it comes to packaging, Tecnifibre has delivered X-One Biphase in style. Each string package features a matte black finish with a gold highlight that bears the string’s name and gauge.

A photograph of the front of Tecnifibre X-One Biphase Package.

The bottom right corner of the package’s front offers a small peek view of the string, while the back of the package showcases the string’s key features and a useful graphic to help players picture the makeup of the tennis string.

A photograph of the back of Tecnifibre X-One Biphase Package.

It’s easy to open the strings with a simple tear from the top left of the packaging, which is perforated.


Overall, I really enjoyed stringing with X-One Biphase.

A quick pre-stretch of the strings removed the limited coil memory that was retained by the strings from packaging and made it very simple to maneuver during stringing.

At first, I did expect the thicker 16 gauge that I playtested to give me a little trouble since it’s a soft multifilament, but I didn’t run into a single problem. I simply made sure to keep a sharp point at the end of the string anytime I ran into a tight spot or blocked hole.

Stringing the crosses was a breeze as the string’s slick outer coating helped it easily slide through the mains. Because X-One Biphase is a softer multifilament, I didn’t experience any issues tying knots.

A photograph of a tennis racquet halfway stung with Tecnfibire X-One Biphase.

A photograph from below a tennis racquet on a stringing machine being strung with Tecnifbire X-One Biphase.

A photograph of a tennis racquet strung with Tecnifibre X-One Biphase from the side.

A photograph of a tennis racquet strung with Tecnifibre X-One Biphase looking down the front of the racquet.

An up-close photograph of the writing on the string of Tecnifibre X-One Biphase strung on a racquet.

An angled photograph of a tennis racquet strung with Tecnifibres X-One Biphase including the triangle Tecnifibre stencil on the strings.

A photograph of the front of a tennis racquet strung with Tecnifibres X-One Biphase including the triangle Tecnifibre stencil on the strings.

X-One Biphase Playtest

Here are a few important stats when playtesting Tecnifibre’s X-One Biphase:

  • String: X-One Biphase 16/1.30mm, natural white
  • Racquet: Wilson nCode nSix-One 95
  • Tension: 60 pounds
  • Forehand: semi-western grip, heavy topspin
  • Backhand: two-handed

Durability 7.5

Overall, I was impressed with the durability of X-One Biphase, which undoubtedly was helped by the fact that I went with the thicker 16-gauge string.

Generally, multifilament tennis strings designed to be soft on the arm and produce a gut-like feel tend to lack durability to a degree, which is simply a tradeoff that comes with the territory when you go with this family of tennis strings.

However, I was happy to find that compared with other multifilament strings I’ve playtested, X-One Biphase held up well, especially under the heavy topspin of my forehand, which is frequently the cause of broken strings for me.

I went with the thickest gauge because I’m a chronic string breaker, so I appreciate the extra life that this gauge provided me. It turned out that I was happy for doing so, as some slight notching in the strings was apparent even after an hour of play.

I did eventually break the strings after eight hours of play, but I felt that for the type of string, this was a great life expectancy, especially considering my style of play.

Helpful Tip
The durability of your tennis strings is dependent on a wide range of factors, including the gauge, or thickness, of the string, the type of grip you hold for your groundstrokes, how hard you hit, the tension you string at and other elements even including the weather.

As you evaluate tennis strings and the importance of durability compared with other factors like comfort, it’s important to consider your style of play. A big-hitting Division 1 college-level player may find a particular string doesn’t hold up well to their game, but that doesn’t mean the string isn’t durable, especially relative to other strings in the same family.

With tennis strings, it’s frequently about tradeoffs, so make sure you weigh durability appropriately against other factors like comfort.

Comfort 8.7

What X-One Biphase lacks in durability to a small degree, it completely makes up for in comfort, thanks to Tecnifibre’s proprietary polyurethane PU 400 and the cushiony Elastyl fibers that make up 50 percent of the string’s composition.

The shock absorption of the string was apparent from my first stroke, and it was delightfully forgiving even with the higher 60-pound tension that I used to control some of the power.

I specifically recall one low forehand that I dug out and hit off-center outside of the sweet spot. I was surprised by how gentle it was on my arm compared with the shock that I might have felt with a more durable polyester string.

All in all, X-One Biphase is a super comfortable tennis string that would be a great fit for anyone suffering from tennis elbow or simply looking to reduce shock and vibration to their arm, perhaps with a stiffer racquet frame.

Power 9.2

If there’s one thing that’s going to surprise you about X-One Biphase, it’s the string’s raw power – a feature that made it super fun to use.

Based on Tecnifibre’s specs and some initial research, I expected it to bring plenty of power, so I intentionally strung it at a higher 60 pounds to maintain a bit more control and bring the power level down a bit. However, even at the higher tension, the extra pop was still apparent.

Generating extra pace when hitting felt automatic, and I never felt like I had to force the ball over the net. Where I really enjoyed the power was on my serve, where I was able to crank it up, and the ball would jump off the strings.

Helpful Tip: If you’re at all concerned about the added power of X-One Biphase, I’d encourage you to up the tension a bit. My approach would be to use X-One Biphase as part of a hybrid setup with control-oriented mains.

Control 7.5 & Spin 6.8

As I was getting comfortable with X-One Biphase, one of the challenges that I did find with my groundstrokes was that the string didn’t have the grip that I’m used to with some of the hybrid string setups that I’ll use.

As a result, I found a few groundstrokes sailing a few feet long, so I had to adjust and focus on generating more topspin to help keep the ball in play.

After about an hour of hitting and once the strings started to settle a bit, it wasn’t an issue. However, similar to dropping the power level a bit, players who hit with a lot of topspin and expect that extra bite from their strings would likely want to string X-One Biphase as part of a hybrid string setup.

Another option would be to drop down to the 17 gauge strings, which should provide you with a bit more grip, although a heavy topspin player might avoid this due to a decrease in durability and life expectancy of the string. If price isn’t much of an issue, then this might be an excellent option for you.

Touch 8.6

Along with X-One Biphase being an incredibly comfortable string to play with, I found it to be highly responsive, which might be a little counterintuitive with the high power the string offers.

The great touch of the string was, not surprisingly, most apparent at the net hitting volleys, where I felt like I had plenty of control and could easily direct the ball wherever I wanted.

Tension Stability 8.8

Overall, I felt like X-One Biphase did a terrific job of holding its tension, which would have been aided by the pre-stretching that I did before stringing.

The settling that occurs after 30 or so minutes of play and is extremely common with many string sets was negligible, and I found the strings continued to hold their tension well throughout my roughly eight-hour playtest.

String Movement 8.7

This one was a bit of a surprise for me. I expected the strings to move much more than they did. After about 15 minutes of play, the strings had barely even budged.

The higher string tension helped limit string movement, but typically I find that my forehand is good for pushing the strings all over the place. Even after a full hour of play, there was less movement compared with other multifilaments.

Wrapping Up

Have you used Tecnifibre X-One Biphase? We’d love to hear about your experience in the comments below. Of course, if you have questions we’d love to hear from you too!

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15 replies
  1. John Brins
    John Brins says:

    I have used this string for about two years and have found it to be the best string for me. As reported the power is very high and the comfort is amazing. I had some arm discomfort prior to using this string but none since. I have used almost every string in the book over 25 years of tennis and I feel that this truely is the best string next to gut. It’s a little costly but in my opinion well worth it.

    • TennisCompanion
      TennisCompanion says:

      Hi John! Thanks so much for the comment and for sharing your thoughts! It’s great to hear that X-One has been an awesome tennis string for you and even better to hear that it has helped with your arm discomfort. The fact that X-One has performance enhancing qualities along with helping reduce physical discomfort certainly helps make this string stand out from the crowd.

      ~ All the best, Jon

  2. Tietzen
    Tietzen says:

    Jon: I am still playing with half natural gut but will give it a try. It might be great with half gut too. still use the 6.1 I gave you?? best PT

    • TennisCompanion
      TennisCompanion says:

      Hey, Tietzen. Thanks for stopping by! X-One Biphase is a great synthetic alternative to natural gut and I think it would absolutely worth a try for you. One the great benefits you’d hopefully find using X-One as a hybrid with natural gut is that you should save yourself some cash along the way. As far as the racquet goes, I bought these years ago so you might have me mixed up with another Jon ;)

      ~ All the best, Jon

  3. Chris Burt
    Chris Burt says:

    I have used it; long term wrist problem that has resolved using a heavier racquet and a multi filiment like this;
    I like the string but believe the Tecnifibre NRG 2 is better; recently ,been using a Yonex poly ,the 125 Tour;no wrist problems and the benefit of a poly; seems to lasts longer. Cheaper too.

    Good string review.

    • TennisCompanion
      TennisCompanion says:

      Hi, Chris! Thank you for your comment and for your insights – super helpful and always welcome! Really happy to hear that you were able to resolve your wrist problem with a heavier racquet and a multifilament like X-One Biphase. As for NRG2, it’s another fantastic multifilament tennis string from the Tecnifibre family with some similar qualities to X-One.

      As for the Yonex Poly 125 that you’re using, yes I would expect that it’s a more durable tennis string as polyester tennis strings tend to hold that quality. Generally speaking, you’ll end up with more durability and control, but most players will find they sacrifice comfort while also seeing a big drop in power. Of course, that isn’t a bad thing… it really all depends on a player’s expectation of their tennis string and their goals out on the tennis court. Good info and thanks again for sharing your experience.

      ~All the best, Jon

  4. Mai
    Mai says:

    I have been playing with NRG 2 18 & X-One Biphase 17, but now I’d like to do a hybrid using these two strings. I am thinking of having X-one be on the mains at 53 and NRG 2 on the crosses at 50. For single string, I play at 50. What do you think? Will this hybrid be too much power?

    PS. I have a persistent tennis elbow and these strings offer me the needed comfort and power.

    • TennisCompanion
      TennisCompanion says:

      Hi there, Mai! Thanks for posting your question! Based on the fact that you have tennis elbow and are looking for a string setup that offers you comfort and power I think stringing X-One Biphase at a lower 17 gauge in the mains and NRG2 18 in the crosses is totally reasonable. You’ll most likely find that this combination continues to offer you high comfort, decent durability with the lower gauge X-One in the mains, and I don’t think you’ll find that the hybrid of these two strings will be overpowering as both strings have a similar power rating.

      A few questions that might help me be a bit more thorough in my answer are:

      1. What is your #1 goal with moving from a single string to a hybrid?
      2. Is there a feature of X-One Biphase and a feature of NRG2 that you enjoyed and therefore were hoping to combine to get the best of both worlds?
      3. What type of racquet are you using?

      ~ All the best, Jon

      • Mai
        Mai says:

        Thank you, Jon, for the response. Here are my answers to your questions:

        1. I am hoping that using the NRG2 18 crosses will allow me more spin. That would prevents my shots to go long (The strings come with fair amount of power).

        2. X-One Biphase and NRG2 offer me the comfort I need for elbow problem. I enjoy volley a whole lot more with these strings because of the exceptional feel.

        3. Head Prestigez

        Thank you again, Jon. If there’s a better option for hybrid, please feel free to comment. I Look forward to hearing from you.

        Best wishes,


        • TennisCompanion
          TennisCompanion says:

          Mai, thanks for getting back to me.

          Personally, I don’t believe stringing X-One and NRG2 as a hybrid setup will provide you with increased spin potential because neither of these strings is inherently geared towards helping players generate spin. If you were looking for more spin my first recommendation would be to maintain X-One Biphase or NRG2 in the crosses of your racquet and then find a polyester tennis string to help with the spin in the mains, but it’s a tradeoff because you will be sacrificing a level of comfort.

          If you were to give this a shot two polyester tennis strings that come to mind are Babolat RPM Blast & Head Lynx. Both are low powered, provide excellent access to spin, and deliver above average comfort relative to other strings in this family.

          On the other hand, if you wanted to keep it in the Tecnifibre family of tennis string I’d suggest you go with Tecnifbire’s Black Code, which is a fantastic string for added spin and constructed to provide a level of comfort. However, I think you’ll find RPM Blast and Lynx to be a bit easier on your arm.

          I realize that might not be the exact answer you’re looking for but I’d rather give you an honest answer based on my experience.

          ~ All the best, Jon

          • Mai Bui
            Mai Bui says:

            Good morning, Jon.

            Thank you so much for the response. I hope you don’t mind if I have two follow up questions:

            1. What gauges would you recommend for the hybrids you’ve mentioned? Tensions? Right now, I am hitting 52 with X-one but thinking of going up to 55.

            2. IF I were to use X-one as mains and ploy as crosses, I have same questions as number one. What do I get out of this set up?

            Many thanks again, Jon. Have an awesome day.


          • TennisCompanion
            TennisCompanion says:

            Hey Mai,

            No problem! This is great conversation :)

            Question #1
            For your first question around gauge, I’d recommend you check out my article on Tennis String Gauge & It’s Impact on Performance. Basically, it’s a trade off between durability and spin potential. The lower the gauge or thicker the string the more durable and generally speaking the less feel/spin. The higher the gauge the less durable and more feel/spin you’ll get.

            For me personally, I’d string X-One a little bit thicker at 16 gauge and one of the polyesters at 17 gauge. I tend to break a lot of strings which can get expensive so I compensate for that with the higher gauge. If I was focused entirely on performance I’d string X-One at 17 gauge and the polyester at 18 gauge.

            As for tension, you may want to check out my article on Enhance Your Game with the Right Tennis String Tension. For X-One you probably don’t need to change that tension but if you do increase the tension you’ll be increasing control and decreasing power. My thought would be to stick with 52 if you’re comfortable with that to start.

            For the polyester, you’re going to want to consider dropping the string tension 5-10% from your typical 52 lbs. A good place to start might be around 49 lbs or roughly 6% lower than your 52 lb tension. Polyester strings are stiffer and tend to perform well at lower tensions, but with a hybrid setup, I’d tend to avoid dropping the polyester string too far where I’ve found things can get a little funky when there’s too large a variance between the two different types of string.

            Question #2
            Generally speaking the string you place in the mains will dominate the overall feel of your racquet. Therefore, using the polyester as the mains will provide you with less power and more control/durability. On the other hand, using X-One in the mains will provide you with more power, comfort, feel and subsequently less control/durability.

            Looking back at one of my previous comment above it looks like I minced my words. I suggested X-One in the crosses and the polyester in the mains. Based on your comments about your elbow problem you’d likely be better off with X-One in the mains and the polyester in the crosses. Sorry for any confusion there.

            In summary, here’s my recommendation – of course, hopefully, based on the information I provided you can tweak this to your preference if needed ?

            • X-One at 16 gauge in mains at 52 lbs
            • Polyester at 17 gauge in crosses at 49 lbs

            ~ All the best, Jon

    • TennisCompanion
      TennisCompanion says:

      Hi, Anant! Thank you for your comment. You can find the string here on Amazon. Hopefully, that’s what you’re looking for. If not, feel free to submit another comment and I’ll be more than happy to see if I can help.

      ~ All the best, Jon

    • Mai
      Mai says:


      Once you give X-One Biphase or NRG 2 a try, you’ll find it nearly impossible to go back to your regular string. The strings are soft with power and great feel. If you have a long and aggressive swing with heavy top spin, I’d recommend the lower gauge.

      Have fun,



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