Tennis Industry magazine


Playtest: Tecnifibre Black Code 4S 17

By Greg Raven

Black is back. Tecnifibre Black Code 4S is a geometric monofilament polyester with a square cross-section. Like the original Black Code, Black Code 4S is produced using Thermocore Technology, a process that varies temperature in stages during manufacturing, allowing a softening of the matrix’s structure. According to Tecnifibre, this gives the string higher flexibility for greater shock absorption and reducing vibration.

Tecnifibre tells us that 4S stands for:

Spin — four sides as opposed to five in the original Black Code (see the July 2009 issue).

Speed — 20 percent more power than Pro Redcode (see the September 2006 issue).

Stability — The same tension maintenance as Razor Code (see the April 2013 issue).

Strength — 15 percent more durable than Black Code.

Tecnifibre developed Black Code 4S for high-level and competition players using racquets weighing more than 300 grams, or 10.4 oz., who are physically strong and want a string that provides spin, power and more durability.

Black Code 4S is available in 16-, 17-, and 18-gauge in black. It is priced from $14.95 per 40-foot set, and $189 per 200-meter reel. For more information or to order, contact Tecnifibre at 800-301-7878, or visit

In the Lab

We tested the 17-gauge Black Code 4S. The coil measured 40 feet, 4 inches. The diameter measured 1.22 mm prior to stringing, and 1.18 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 (16 × 18 pattern) on a constant-pull machine.

After 24 hours (no playing), string-bed stiffness measured 74 RDC units, representing a 4 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 has a stiffness of 217 and a tension loss of 11.67 pounds, while Tecnifibre Black Code 4S 17 has a stiffness of 199 and a tension loss of 16.69 pounds. Black Code 4S 17 added 16.4 grams to the weight of our unstrung frame.

The string was tested for five weeks by 36 USRSA playtesters, with NTRP ratings from 3.5 to 6.0. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. Average number of hours playtested was 29.6.

Tecnifibre recommends stringing Black Code 4S 5 percent looser than a typical nylon string, and we passed this along to the members of our playtest team.

The edges of the string are obvious as soon as you take Black Code 4S out of the package. Although the mains get a little bruised when pulling the crosses, Black Code 4S is not as aggressive on your fingers as some of the other geometrics.

Three playtesters broke the sample during stringing, nine reported problems with coil memory, eight reported problems tying knots, three reported friction burn, and three reported other problems.

On the Court

According to Tecnifibre, the first “S” of the 4S is spin, and our playtest team agreed, giving it the 10th highest rating for spin of the 186 playtests we have conducted for publication. This is the highest spin rating of any Tecnifibre string we’ve tested. Black Code 4S also rated well above average in Durability, Resistance to Movement, and Control. As a result, Black Code 4S overall rated well above average.

No playtester reported premature fraying, peeling, or buzzing, and three reported notching. Three broke the sample during the playtest period, one at 4.5 hours, and two at 12 hours.


Tecnifibre Black Code 4S delivers on its promises, offering more spin potential than any other Tecnifibre string, garnering a higher rating in the Power category than Pro Redcode 16, and testing higher in our lab for Tension Retention than Razor Code 16. And, according to our lab tests, Tecnifibre Black Code 4S is actually softer than our reference nylon.

Playtester comments

“The string had good ball pocketing ability, I was able to take a good cut at the ball and keep it in due to spin. It was easy on the arm and performed probably one of the best ones I’ve tested. If you like to bash from the baseline this is your ticket.” 5.0 male baseliner with heavy spin using Babolat Pure Storm Limited strung at 54/52 pounds LO (Forten Kevlar/Forten Sweet 18/16)

“This is a very good, softer poly string. For a string as durable as it is, it plays and feels great. I do like my poly strings to be a little crisper and to have a little more feel but the durability of the strings helped counter those minuses. Power was low, but spin was high, which made for a great control-oriented string. The string felt a little dull, but not harsh. Off-center shots didn’t send much shock to the arm. I’d have no worries about recommending this string to someone nervous about using poly. Overall this is an excellent string. I’m curious to find out what it is, the price, and see about experimenting with it in a hybrid. I think this string is best suited for advanced players with big, loose swings, people who not only generate their own power but also aim for the lines and the corners. Being conservative with this string caused too many balls to sit up in the center of the court, but I was rewarded by aggressively going for the lines. Swinging away on the return of serve made for some particularly good balls. Going for more spin on the serve was also a treat.” 4.5 male all court player using Wilson Pro Staff strung at 52 pounds CP (Kirschbaum Spiky Shark Black 17)

“Very good string. It had a great feel to it. I was able to generate more topspin.” 5.0 male serve-and-volley player using Babolat Aero Pro Drive GT strung at 57 pounds CP (Babolat RPM Blast 16)

“This is a very comfortable string that plays well right away.” 4.0 male all court player using Prince Premier ESP strung at 58 pounds CP (Prince Tour XP 15L)

“Like the string immediately as I was stringing it. Felt a little like Black Widow but easier to string and less challenging to the hands to pull and feed the string. It held tension well and the feel when I hit the ball was a great experience.” 4.0 male all court player using Wilson Burn S strung at 58 pounds CP (Wilson Revolve 16)

“Besides being one of the most comfortable and durable polys I have played with, the effortless increased spin production is worth stocking this string.” 5.0 male serve-and-volley player using Head Extreme Pro strung at 55 pounds LO (Gamma Live Wire Pro/Gamma TNT 16/17)

“Very sharp edges, lots of spin potential and bite on the ball!” 5.0 male baseliner with moderate spin using Babolat Pure Drive + strung at 50 pounds CP (Babolat RPM Blast/Babolat Xcel 17/17)

“I really liked this string. Not as rigid right off the machine as most polys. Good feel and spin. Comfortable at the net.” 4.5 male all court player using Head Graphene Radical strung at 45 pounds CP (Ytex Quadrotwist 16L)

“I thought it was a good solid string. Not as much pop as some, but easy on the arm and had plenty of spin on ground strokes, volleys, and serves. Really able to get excellent bite on strokes with these strings. Would use this string as well as sell in shop.” 5.0 male all court player using Prince Warrior Tour strung at 55 pounds CP (Dunlop Black Widow 17)

“This was an exceptionally good string in all respects. Stringing this poly was easier than others I have used in that there was not nearly as much coil memory. I was very pleasantly surprised when I first played with the string — other polys tended to be very stiff and had reduced playability/feel and I would feel more vibration in the frame. This string was great from the first ball hit — it achieved very high marks in every category even when compared to the multifilament string I normally use. Then when you consider the string’s resistance to movement and durability, you have a winner all around! I would definitely consider switching to this string!” 4.5 male all court player using Prince O3 Blue strung at 50/48 pounds LO (Tecnifibre NRG2 18/17)

“String was good. I played 12 hours of hard tennis singles matches, etc. So, it was a good string.” 5.0 male all court player using Head Prestige strung at 56 pounds LO (Prince or Tecnifibre Poly/Synthetic Gut 16)

“This is definitely a string that I would recommend to players looking for a poly-type play with a comfortable feel on the arms and elbows. It seems to play somewhere between a poly and synthetic gut but plays a bit softer than poly. I found relatively good control, but not the same as my usual natural gut or Silk setup. I don’t often hit with a lot of spin, but I can generate some decent spin with gut when I try to. I couldn’t generate a lot of spin with this string for some reason. As far as durability, I am not a string breaker with synthetics although I do break gut. However, this string didn’t seem phased at all with the modicum of play that it had received. I feel I could go a lot longer if I continue to play with this string.” 4.0 male baseliner with moderate spin using Prince Hybrid Hornet O3 Oversize strung at 60 pounds LO (Dunlop Silk/Pacific Natural Gut 17/17)

“I thought it played very well and comparable to a lot of the polys I’ve tested. As with most polys, it was unforgiving on off center shots. I didn’t feel that it was a very comfortable string to play with. It was crisp and solid on groundstrokes as well as volleys. I think it’s a great string for big hitters who need the spin potential to help control the ball.” 5.0 male all court player using Wilson Pro Staff RF strung at 48 pounds LO (Luxilon Big Banger Ace/Wilson NXT 18/17)

“From the first hit was a comfortable string with good pliability. Was able to get spin easily. Felt like it gripped the ball. You have to provide your own power.” 5.0 male all court player using Head Graphene Prestige strung at 60 pounds LO (Head Sonic Pro 16)

“Bites the ball well. Slips nicely. More durable than I need!” 5.0 male all court player using Babolat Pure Strike 16x19 strung at 52/50 pounds CP (Babolat VS Gut/Babolat RPM Blast 17/18)

“Overall the string played very well. It was thin and really felt like it was biting the ball, which increased spin. The feel was pretty good, but seemed to go dead just before it broke. Durability was not good. The control and spin creation were both very good.” 6.0 male all court player using Wilson Juice S strung at 52 pounds CP (Luxilon 16)

“This string provided a good combination of spin with a nice sharp edge and durability. The power level was up there as well to allow a player to take less swing and still be able to drive the ball deep into the court. This would also be recommended as part of a hybrid pattern for use with another poly type for added spin and durability.” 5.0 male serve-and-volley player using Wilson BLX Juice S strung at 56 pounds CP (Luxilon 4G 125/Wilson NXT 16/17)

“Higher spin potential with the shape of the string, which I liked. Stiffer string than I am accustomed to so I found a little sacrifice in control and feel, but durability seems to be a plus.” 4.5 male serve-and-volley player using Wilson BLX Two strung at 60 pounds LO (Wilson NXT 16)

“On opening package, the string immediately identified itself as a poly. As such, I was not surprised with moderate coil memory. More of a problem was string bending, then getting tangled when unraveling and preparing string for stringing. I also noticed the thin gauge (17 or 18), which excited me for spin possibilities. After first main string knot was tied, string broke. There was not enough string left to tie a 2nd knot, but fortunately the 1st knot held. Rest of stringing was uneventful, and extra care taken when tying off crosses. I like the thin gauge for bite, helpful for spin. Durability is good. It played surprisingly well as a single string. I think its strength will be as a hybrid in the mains, with a soft multifilament or even natural gut in the crosses. I would love to try it in the mains with Gamma Professional 17 or 18 in the crosses. That would be a killer combination.” 4.0 male all court player using Dunlop Muscle Weave 200g strung at 48 pounds LO (Gamma Professional 17)

“Overall, this string was slightly more challenging to install than the string I frequently use. Due to its shape and consistency, there is potential for friction burn. I found the string to have good spin production, power, and comfort. Control and touch were just average.” 4.0 male baseliner with heavy spin using Babolat Pure Strike strung at 57 pounds LO (Luxilon Savage 17)

“Powerful hitters will enjoy this string because it allows players to hit big with control and confidence. Players at the other end of the spectrum — weaker, finesse players who play with a lot of touch and feel — may find this string too stiff and not easy to tame.” 4.0 female all court player using Prince Warrior L ESP strung at 54 pounds CP (Tecnifibre NRG2 17)

“This string did everything pretty well. While it didn’t quite measure up to RPM or Alu Power fresh off the machine, it remained playable for a much longer time than those strings. The string offered consistent response, good comfort, and surprising tension maintenance for a poly. If priced right, I would consider carrying it.” 4.5 male all court player using Boris Becker Delta Core London Midplus strung at 48/45 pounds CP (Solinco Tour Bite Diamond Rough 17)

“This string allows one to develop a lot of spin. Average polyester string.” 4.5 male all court player using Babolat AeroPro Drive strung at 57 pounds CP (Babolat Origin 17)

“After 8 hours of play, tension dropped down. Ball speed increased along with becoming more comfortable. This string will appeal to older players that like to play the point out.” 3.5 male touch player using Wilson nRage strung at 48 pounds CP (Prince Synthetic Gut with Duraflex 17)

“String required a ‘break-in’ period of about 4 hours before it started to play better. Even strung loose, it didn’t develop sufficient bite or feel for my taste. It required more effort on my part to deliver power and control. It improved once the string flattened out. Probably would be a better string for players that hit short, flat strokes with 110 sq. in. or larger frames. Frequent string breakers that do not over hit would probably enjoy this string.” 4.0 male all court player using Babolat Pure Storm strung at 45 pounds CP (Gamma TNT2 18)

“This is a very brittle string with lots of coil memory. It is definitely a power string I would use with hybrid patterns with a soft woven synthetic in the crosses.” 4.5 male all court player using Wilson BLX Five Lite strung at 53 pounds LO (Wilson NXT 17)

“For me, the strings felt very stiff and lacked touch and feel especially up at the net. For the average player, they lack power. They may be a good fit for a big hitter who needs to tame some of their power down to gain control. The same could be said for someone who needs to bring a powerful racquet back under control.” 4.0 male all court player using Volkl Organix V1 Pro strung at 50/48 pounds CP (Tourna Big Hitter Black 7/Tourna Big Hitter Black Zone 17/17)

“Found the string difficult to string only during the cross stringing as the edges grabbed frequently during the pull through. The string was pliable for a stiff string. Knot tying was similar as other stiff strings. During play, I found that my control suffering as compared my regular strings. Lacked some feel on touch shots. Power was about the same. I noticed notching after 5 hours of play. Overall, not a bad string as I would recommend it for hybrid stringing.” 4.0 male all court player using Wilson Pro Staff RF strung at 59/56 pounds CP (Wilson Stamina/Luxilon ALU Power Spin 17/17)

“This is a nice but average poly. It worked well and didn’t feel harsh or uncomfortable but definitely stiff with the recommended 5% drop in tension. Good stock string.” 4.0 male baseliner with moderate spin using Babolat Pure Drive + strung at 55 pounds CP (Babolat Natural Gut 16)

“Loved how it played, did not love how long it lasted.” 4.5 male all court player using Prince Tour ESP strung at 53/56 pounds LO (Prince Tour XC 17)

“Stiff and boardy. Below average power, feel, and comfort. Other than being durable, it disappointed in all other areas. Would only recommend to chronic string breakers.” 4.0 male baseliner with heavy spin using Dunlop 200G strung at 58/56 pounds CP (Prince Synthetic Gut with Duraflex 16/17)

“I did not enjoy this string. It seemed to lack power even though I strung it lower (58 pounds versus 63 pounds for my normal string), and was unforgiving on off-center hits. I even found the string bothered my wrist and elbow.” 4.0 male baseliner with moderate spin using Pro Kennex Ki 15 PSE strung at 58 pounds CP (Pacific X-Force/Pacific Power Line 18/16)

“My racquet cracked after eight hours of play. I felt like I had to swing harder to keep the ball in play. Serves were strong. Drop shots were inconsistent. If I got under the ball, there was a lot of access to spin. My backhand floated more than average. The sweet spot seemed smaller and the stringbed was unforgiving outside of the sweet spot.” 4.0 male all court player using Volkl Organix 4 strung at 56 pounds CP (Volkl V-Twist 17)

“I will not buy it. I will not use it. I will not stock it. I will not recommend it. If requested to string with it I will charge extra. This string was terrible to weave and the knots did not cinch well. I strung it at 5% less as recommended and should have strung it looser. After 10 hours I could feel it on my arm and wrist. Plenty of spin, but the string stops there. I was unimpressed by the string and I am sure I will be unimpressed by the price.” 4.0 male all court player using Prince O3 Red MP strung at 53 pounds CP (Gamma TNT2 Pro Plus 17L)

Playtester Ratings

Ease of Stringing (compared to other strings)
much easier 0
somewhat easier 4
about as easy 13
not quite as easy 15
not nearly as easy 2
Overall Playability (compared to the string played most often)
much better 0
somewhat better 7
about as playable 5
not quite as playable 15
not nearly as playable 7
Overall Durability (compared to other strings of similar gauge)
much better 6
somewhat better 14
about as durable 11
not quite as durable 2
not nearly as durable 1
Rating Averages
From 1 to 5 (best)
Playability 3.3
Durability 4.0
Power 3.3
Control 3.6
Comfort 2.9
Touch/Feel 2.9
Spin Potential (10th overall) 3.9
Holding Tension 3.3
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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