Tennis Industry magazine


Playtest: Isospeed Professional Classic 17

By Greg Raven

Isospeed Professional Classic is a coreless multifilament, where the filaments are Isospeed’s trademarked polyolefin ribbons. Isospeed tells us that Professional Classic is designed for players looking for gut-like performance in terms of speed and arm protection.

Professional Classic is available in 17 gauge (1.20) in natural. It is priced from $12 per set. Reels are not available. For more information or to order, contact Isospeed at 866-554-7872, or visit Stringers who are in North America can also contact Isospeed distributor Tennis Warehouse at 800-883-6647, or check out the Isospeed collection at

In the lab

The coil measured 40 feet. The diameter measured 1.22-1.25 mm prior to stringing, and 1.18-1.23 mm after stringing. We recorded a stringbed stiffness of 75 RDC units immediately after stringing at 60 pounds in a Wilson Pro Staff 6.1 95 (16 x 18 pattern) on a constant-pull machine.

After 24 hours (no playing), stringbed stiffness measured 64 RDC units, representing a 15 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. Professional Classic added 16 grams to the weight of our unstrung frame.

The string was tested for five weeks by 45 USRSA playtesters, with NTRP ratings from 3.0 to 6.0. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. Average number of hours playtested was 23.7.

Out of the package, Isospeed Professional Classic feels thick and substantial, which is unusual for a 17-gauge string. Our clamps left some marks at the clamping points. Isospeed recommends waxing the strings with a piece of wax paper before stringing, but we did not send that instruction to the members of our playtest team. Without waxing, the string can look a little “beat up” after stringing, especially if you are in a hurry.

One playtester broke his sample during stringing, 15 reported problems with coil memory, one reported problems tying knots, and 16 reported friction burn.

On the court

Isospeed Professional Classic impressed our playtest team. Its best result was Spin Potential — a category for which our playtesters are typically stingy with praise — where Professional Classic earned a 15th-place finish out of the 115 strings we’ve playtested for publication to date. In just about every other category, our playtest team members were only slightly less generous, scoring Professional Classic well above average in Playability, Durability, Power, Control, Touch, Comfort, and Resistance to Movement, and above average in Tension Retention. As a result, the overall average score for Professional Classic was also well above average, and good enough to earn it a top-20 finish.

Five playtesters broke Professional Classic during playtesting, one at nine hours, one at 12 hours, two at 15 hours, and one at 25 hours.


Isospeed is not a famous brand name in the United States, but its strings seem to be developing a cult following. Given our playtest teams’ positive responses to Professional Classic 17 and Professional 17 (RSI, June 2007), it’s not difficult to see why. Our playtesters even thought Professional Classic compared favorably to their favorite string, which is quite a compliment.

One reason for this may be Professional Classic’s category-to-category balance. No matter what aspect of string response you are seeking, Professional Classic 17 seems to have it, without sacrificing in other areas. This could be a good string to have on hand for those customers who don’t know what they want, but they want something good.


“This string is a hard-hitter’s dream. The low power level makes this a good option for those who prefer high head speeds. For such a comfortable string, the response is surprisingly crisp and predictable.” 3.5 male all-court player using Völkl Tour 10 strung at 60 pounds LO (Gamma Professional 17)

“This is a durable string with a crisp response. Recommended to hard hitters who prefer some playability.” 5.0 male all-court player using Prince O3 White strung at 60 pounds CP (Prince Synthetic Gut w/Duraflex 16)

“If you want playability, look no further. This string can do it all. The sticky exterior makes for very little string movement. This adds control and durability to what is a very comfortable string bed. Power level is low, making this an appealing choice for big hitters.” 4.5 male all-court player using Wilson nSix Two strung at 61 pounds LO (Polyester/Nylon 17)

“Pulling crosses is made slightly difficult by the sticky coating. Once you get on the court, however, the comfort, control, and playability take over.” 5.5 male all-court player using Wilson nSix One Tour strung at 57 pounds LO (Ashaway Crossfire 17)

“After some tension loss, this string plays very well. Some pre-stretching would probably make this play well right out of the box. There is pronounced ball pocketing, making it very easy to “grip” and spin the ball. Topspin and slice are a cinch.” 5.0 male all-court player using Head FXP Prestige Team strung at 63 pounds LO (Babolat VS Touch 15L)

“After 16 hours, there is noticeable tension loss. However, after the break-in period, it plays better and pockets the ball nicely. This is a very comfortable control string. Great for touch players and those with tender tendons.” 4.5 male all-court player using Yonex RDX 500 Mid strung at 60 pounds CP (Babolat Xcel/Luxilon Alu Power 17/16L)

“This string has three very prominent features: high dwell time, comfort, and low power. I have the sensation that I’m catching and throwing the ball back to its target. I think I’ve finally discovered the opposite of “spraying.” The ball feels like its getting sucked into a pillow. It will appeal to players who favor a deep thud over a ping.” 3.5 male all-court player using Völkl DNX 8 strung at 58 pounds CP (Head Intellistring 16)

(Strings normally used by testers are indicated in parentheses.)

Playtester ratings

(compared to other strings)
Number of testers who said it was:
much easier 1
somewhat easier 1
about as easy 19
not quite as easy 21
not nearly as easy 3
(compared to string played most often)
Number of testers who said it was:
much better 1
somewhat better 14
about as playable 8
not quite as playable 17
not nearly as playable 2
(compared to other strings of similar gauge)
Number of testers who said it was:
much better 1
somewhat better 16
about as durable 19
not quite as durable 6
not nearly as durable 1
From 1 to 5 (best)
Playability 3.6
Durability 3.7
Power 3.4
Control 3.6
Comfort 3.6
Touch/Feel 3.4
Spin Potential (15th best to date) 3.5
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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