Tennis Industry magazine


String Playtest: Kirschbaum Pro Line II Rough 1.25

By Greg Raven

Kirschbaum Pro Line II Rough is a third-generation co-polyester string with a roughened surface designed for extra spin, with balanced precision and power. According to Kirschbaum, the string comes from a development of new materials and mastery of the low-temperature fusion at which they are processed, resulting in a feel that’s similar to a synthetic gut regarding playability, but with all the virtues of polys. It also does not move and will hold its tension, the company says. Pro Line II Rough is suited for competitive players of all ages.

Pro Line II Rough is available in 1.20 mm, 1.25 mm and 1.30 mm in black only. It is priced from $9 for 40-foot sets, and $109 for reels of 660 feet.

For more information on any of these strings, or to place an order, contact Kirschbaum at 866-443-4428, or visit

In the Lab

We tested the 1.25-mm Pro Line II Rough. The coil measured 40 feet, 11 inches. The diameter measured 1.25 mm prior to stringing and 1.23 mm after stringing. We recorded a string-bed stiffness of 69 RDC units immediately after stringing a Wilson Pro Staff 6.1 95 (16 x 18 pattern) at 60 pounds on a constant-pull machine.

After 24 hours (no playing), string-bed stiffness measured 62 RDC units, representing a 10 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 an 8.3 percent tension loss. In lab testing, Prince Synthetic Gut Original has a stiffness of 217 and a tension loss of 11.67 pounds, while Kirschbaum Pro Line II Rough 1.25 has a stiffness of 194 and a tension loss of 19.56 pounds. Pro Line II Rough 1.25 added 15.7 grams to the weight of our unstrung frame.

The string was tested for five weeks by 34 USRSA playtesters, with NTRP ratings from 3.5 to 5.5. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. The average number of hours playtested was 23.8.

Kirschbaum does not provide a tension recommendation, so we allowed our playtesters free rein. Pro Line II Rough does have some coil memory. The surface texture creates extra drag through grommets and when pulling crosses through mains — along with some noise. It is not difficult, just different. We almost ran out of string on an oversize racquet, so perhaps the extra density implied by the high weight of the string helps it withstand stretch.

No playtester broke the sample during stringing, eight reported problems with coil memory, five reported problems tying knots, two reported friction burn and eight reported other problems.

On the Court

Pro Line II Rough promises spin — and our playtest team agreed, rating it the seventh best string in the Spin category of the 192 strings we have playtested for publication. Hand-in-hand with this, the playtesters also rated Pro Line II Rough the 15th best string in the Control category.

Pro Line II Rough also garnered an excellent rating in Durability, and was judged to be well above average in Resistance to Movement and Tension Retention. Accordingly, the overall score is well above average.

No playtester reported premature fraying or peeling, one reported buzzing and five reported notching.


If you have customers looking for a spin string, Pro Line II Rough is much easier to install than some of the geometric spin options on the market. It has all the characteristics needed by players who generate their own power, and with three different gauges, you can dial to your customers’ specific needs.

Playtester comments

“The string was very playable. For the power that I got out of the string I thought there was a lot of control and the ball seemed to move through the court easier. Really enjoyed the string.” 5.0 male all court player using Head Prestige strung at 55/57 pounds LO (Prince Synthetic Gut 16)

“Easy to string, easy on the arm, and lots of control and touch.” 5.0 male serve-and-volley player using Wilson Pro Staff RF strung at 52 pounds LO (Gamma Live Wire Pro 16)

“I thought the string was excellent with ball pocketing and easy access to spin. It also maintained tension for a longer period and was a good spin producing string.” 5.0 male baseliner with heavy spin using Babolat Pure Storm Ltd strung at 53/51 pounds LO (Forten 17)

“While a little challenging to string due to the texture of the string, the spin and playability were excellent.” 4.0 male all court player using Wilson Burn 100S strung at 50 pounds CP (Wilson Black Savage/Wilson Sensation 16/16)

“This was a really neat string. I would purchase it in a minute when available. It has great spin potential and yet had a great touch and feel. The durability was also very good with plenty of power to boot. This could be a great string for a hard hitter and a player looking for some extra touch. Excellent in many ways.” 5.0 male using Wilson Juice 100S strung at 62 pounds CP (Wilson NXT Duo II/Luxilon Adrenaline 17)

“This string seemed to be a poly-based string which I generally don’t use, especially in a full string bed. However, at lower tensions, even in my 18x20, 98 sq. in. frame, this string was pleasantly playable with respect to control, power, and comfort. It held tension very well (about 10% loss in the 20+ hours of play) and installed easily. It was easy on the arm as well … I think I found my new string!” 4.0 baseliner with moderate spin using Dunlop 4D 300 Tour strung at 51 pounds LO (Pacific Natural Gut/Ashaway Dynamite 16L/17)

“I enjoyed playing with this string from the first struck ball. It had a nice blend of all the things you look for in a string. Good balance of the big three items of any string; power, control, and comfort. This string has it all.” 4.5 male all court player using Prince Tour 100 ESP strung at 52/56 pounds LO (Prince Tour XP 17)

“String played very well while testing, it was comfortable and very forgiving during play. It felt very good while serving, giving the ball extra spin and easy-to-control placement. Volleys were made easy by the string’s softness; I had good control. Overall this was a very nice string compared to the hybrid version I use.” 4.0 male serve-and-volley player using Prince Warrior Textreme strung at 52/55 pounds LO (Prince XT/Prince Premier Touch 18/16)

“I thought it was a good string for an all court player. It was comfortable to volley with as well as to hit groundstrokes. I like the spin potential that it gave me. It was a little easier to spin the ball with this string than the hybrid stringing that I use. I also thought it gave me the potential for more power, but without the lack of control. It was a good string to play with.” 5.0 female all court player using Wilson Pro Staff strung at 48/48 pounds LO (Luxilon Big Banger Timo/Wilson NXT 18/17)

“Very good spin production due to textured surface. Average power and comfortable on all types of shots. Textured surface flattened out at clamps and tension head.” 4.0 male all court player using Prince TT Viper strung at 60 pounds LO (Gamma Ruff 16)

“Spin potential was very good. Great for touch and drop volleying. I was able to swing out and use more aggressive topspin. All of these great attributes came at the price of comfort and power. It is a well-balanced string with great durability. It performs better in warmer temperatures.” 4.0 male baseliner with heavy spin using Dunlop 200G strung at 64/58 pounds CP (Prince Synthetic Gut with Duraflex 18)

“Great string for a 3.5 player because of how comfortable it is and easy to play with.” 4.0 male all court player using Prince Warrior strung at 55 pounds CP (Prince Tour XP 17 )

“The string was the most difficult string I have ever used to string a racquet because of the roughness of the surface of the string and coil memory. Due to the roughness of the surface, I strung this 4 to 6 pounds lower than I normally string a racquet. After stringing, the racquet had a string bed stiffness of 71. I always pre-stretch string. I would have assumed this string would play like a board but it was unusually playable.” 4.0 male all court player using Head Ti.6 strung at 52 pounds CP (Prince Synthetic Gut w/Duraflex/Gosen OG Sheep 17/17)

“Good overall string for all levels. Gives you a bit more bite to the ball because of the texture. Has good overall feel and spin. Power was a little lacking.” 5.0 male all court player using Head Prestige Pro strung at 57 pounds LO (Head Sonic Pro 16)

“Initially the string provided a very solid feel and was very responsive on touch shots. However, after about 15 hours of play the bed softened and balls started carrying long. This was correctable and as the strings were so comfortable it was worth playing through. Big hitters will need to adjust their tension but the playability should make it worthwhile. Soft hitters should find this to be a nice long lasting string with negligible change in performance over time.” 4.0 male all court player using Prince Red LS strung at 55 pounds CP (Gamma TNT2 16)

“Great spin potential, though I personally would blend with a multifilament to soften it a bit.” 5.0 male baseliner with moderate spin using Babolat Pure Drive + strung at 50 pounds CP (Babolat RPM Blast/Babolat Xcel 17/17)

“Really enjoyed playing with this string. The textured rough finish allowed for great spin control. The string, though somewhat stiff, played with a soft touch and was friendly on the arm. Though string tension was fading, I found I still had good control up to the 15th hour of play. I would consider adding this string as a new addition to my other strings.” 4.0 male all court player using Wilson Pro Staff RF strung at 59/56 pounds CP (Wilson Synthetic Gut Duramax/Luxilon 127 spin 17/16L)

“Excellent string. I’m guessing it’s a co-poly. Great combo of power, control, and spin. The downside is that the string is a bit dull, but not stiff, and lacks feel. I wouldn’t recommend this string to touch players, but I would highly recommend it to power baseliners. The string notched fairly early, but I didn’t notice that much loss in performance. The string, of course, has a lot of texture and I’m curious how it would work in a hybrid with synthetic gut. Due to the texture, there was some amount of extra friction while stringing, but nothing major. Overall, a first-class string. I’m looking forward to finding out what this is.” 4.5 male all court player using Wilson Pro Staff strung at 55 pounds CP (Volkl Classic Synthetic Gut/Topspin Cyber Blue 16/17)

“The string provided a fair amount of control. I did not feel much pop or power, but enjoyed the amount of spin I could put on the ball. I could really get a good amount of backspin bite on approach shots and spin on serve. The test string seemed to hold tension well, but in the last 5 to 8 hours the string lost a fair amount of punch. I would like to use it as the mains in a hybrid with a softer, livelier string in the crosses. Should provide a nice combination of spin and punch.” 5.0 male all court player using Prince Textreme Warrior strung at 50 pounds CP (Prince Tour XP/Babolat Spiraltek 16/16)

“This string was a little more difficult to string and took longer due to its stiffness. Nevertheless, I found this string very playable from the first hit - playability was very good and I was pleasantly surprised to find that there was no detectable shock or vibration as I have found with strings of similar composition. Power was not as great as the string I normally use, but overall the string was very good on all other qualities evaluated. The strings never moved and there was no evidence of wear even after 20 hours of singles play - durability is exceptional. I would recommend this string to anyone who wants an excellent playing string with durability.” 4.5 male all court player using Prince O3 Red strung at 57/55 pounds LO (Tecnifibre X-One BiPhase/Tecnifibre NRG2 18/18)

“This is a good overall string for feel, control, and power. Its slight texture helps ‘bite’ the ball for more spin potential.” 4.0 female all court player using Prince Warrior 100L ESP strung at 56 pounds CP (Tecnifibre NRG2 17)

“The string is a little stiff, but not too bad. The texture added to the spin potential but that did not last for the duration of this durable string. A good string if you generate your own power and would like a little assist in making spin.” 4.0 male baseliner with moderate spin using Babolat Pure Drive + strung at 55 pounds CP (Babolat Natural Gut 16)

“Nice string overall. Gave me some good spin, particularly in the first several hours. The texture was interesting. I’m not sure whether it really adds much but I did notice a small drop off in spin after it smoothed out a bit. My arm tolerated this string also.” 4.0 male all court player using Prince Textreme Tour strung at 45 pounds CP (Prince Tour XT 17L)

“String is designed for spin at the expense of comfort. Good for young players who desire spin.” 4.5 male all court player using Babolat Pure Aero strung at 57 pounds CP (Babolat Origin 17)

“Bites the ball well. It might have felt more playable if I had strung it at a lower tension. I do not see using this as a hybrid with a multifilament or gut, because the texture and friction would saw through the gut or multi. As an all-poly string bed, I see it selling to those who like a crisp feel with less slippage than other polyester monofilaments.” 4.5 male touch player using Donnay Formula strung at 55 pounds CP (Babolat VS Touch/Babolat RPM Blast 16/18)

“This string did not hold tension very well. I strung it pretty loose as I do with the poly strings. Felt really springy. Hard to control. I like the texture though. Maybe I just didn’t string it tight enough.” 4.5 male all court player using Prince Warrior 100L strung at 55 pounds LO (Prince Poly 16)

“I immediately felt the control of the power I generate. I was able to hit out without the pain of other monofilament strings. There was a solid ‘pop’ on groundstrokes and overheads. What I gained in control, I lost in feel, particularly on drop shots. The string was great from the baseline for control, but as I moved forward, I lost the directional control that I usually have with multi-filament strings.” 4.0 male all court player using Volkl Super G 4 strung at 59 pounds CP (Volkl V Twist 17)

“Installing the string was easier than expected, I thought it might be more difficult with the added texture I noticed when I took it out of the package, but it was no more difficult than my usual strings. I got good spin using this string. Power, control, and playability were just average. I was not pleased with the feel/touch - I did not have the usual ‘connection’ to the ball I am used to having with other strings I’ve used.” 4.0 male baseliner with heavy spin using Yonex Vcore Duel G strung at 58 pounds LO (Luxilon Savage/Solinco Tour Bite 16/17)

“I did not like the string at the beginning, but after about 6 hours of play, I started liking it a whole lot better. The strings felt dull at the beginning but got better after breaking them in. The strings favor a big hitter who can supply the power. The cross strings were difficult to weave since they tended to grab onto the mains.” 4.0 male all court player using VolklOrganix Super G 10 295g strung at 55 pounds CP (Volkl Cyclone/Tourna Synthetic Gut Armor 19/17)

“Nothing special. Another mundane poly that did not feel any better than any other.” 5.0 male all court player using Prince EXO3 Tour ESP strung at 50 pounds CP (Prince Premier Power 17)

“Good texture to the string and easy to install. The feel wasn’t great, but the spin potential was! The durability was poor. Overall, if you wanted a thin string, with some bite to generate spin, this would be a great string. However, in an open string patterned frame, it is not a good string at all.” 5.5 male all court player using Wilson Juice 100S strung at 50 pounds CP (Luxilon 4G 17)

“This string was below average in both control and power.” 4.0 male baseliner with moderate spin using Pacific Raptor strung at 57 pounds CP (Pacific Premium Power 16)

“Very low powered string. More difficult (than normal) to string due to the string texture.” 3.5 male all court player using Wilson BLX Blade strung at 55 pounds LO (Wilson Natural Gut 16)

“Too much kinking when you get to the end of the crosses, and the sound of the strings rubbing as you pull the crosses through is ear-shattering like fingernails on a slate chalkboard. Adequate from the baseline and for serves, but I felt nothing positive on my volleys. I also felt the strings were loosening even with the light amount of play. Definitely not a string for me.” 4.0 male all court player using Prince O3 Red strung at 56 pounds CP (Gamma TNT2 Pro Plus 17L)

(Strings normally used by testers are in parentheses. For more tester comments, visit

Playtester Ratings

EASE OF STRINGING (compared to other strings)

much easier: 2

somewhat easier: 5

about as easy: 11

not quite as easy: 14

not nearly as easy: 2

OVERALL PLAYABILITY (compared to the string played most often)

much better: 0

somewhat better: 8

about as playable: 8

not quite as playable: 14

not nearly as playable: 4

OVERALL DURABILITY (compared to other strings of similar gauge)

much better: 6

somewhat better: 14

about as durable: 12

not quite as durable: 2

not nearly as durable: 0


From 1 to 5 (best)

Playability: 3.4

Durability: 4.2

Power: 3.1

Control: 3.8 (15th overall)

Comfort: 3.3

Touch/Feel: 3.1

Spin Potential: 4.1 (7th overall)

Holding Tension: 3.5

Resistance to Movement: 3.8

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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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