Tennis Industry magazine


Playtest: Gamma Zo Sweet 17

By Greg Raven

Gamma Zo Sweet is a 17-gauge hybrid that combines Gamma’s Zo Power coated monofilament polyester in the mains and its TNT² nylon in the crosses. According to Gamma, Zo Power is an ultra-playable polymer alloy, manufactured as a co-extrusion fiber with a wear-resistant surface surrounding the high-energy core. The TNT² has an Elastalon center core and outer wraps, with a “pearl” coating to enhance durability. Each of these strings is enhanced by Gamma’s TNT² technology.

Gamma Zo Sweet

Gamma claims that its proprietary TNT² process changes the highly-aligned chains that normally occur in string material in such a way that millions of new intermolecular bonds are created among the long-chain molecules, creating more cross-linking for a stronger, tougher, and yet more flexible material.

Gamma designed Zo Sweet for players looking for a softer feel than that generally found in an all-polyester stringbed, but with more durability and stiffness than that generally found in an all-nylon stringbed. This target group are usually the intermediate to advanced players with fast swing speeds. According to Gamma, the addition of the TNT² cross strings softens the stringbed so that, without sacrificing all control, a player will still be able to generate additional power yet have a string that is easier on the arm.

Zo Sweet is available only in 17 gauge in white/natural. It is priced from $15.95. For more information or to order, contact Gamma at 800-333-0337, or visit the Gamma Sports website.

In the lab

The coils measured 23 feet 7 inches (Zo Power mains) and 21 feet 5 inches (TNT² crosses). The diameters measured 1.22 mm (Zo Power) and 1.26 mm (TNT²) prior to stringing, and 1.19 mm (Zo Power) and 1.19 mm (TNT²) 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 (16×18 pattern) on a constant-pull machine.

After 24 hours (no playing), the string-bed stiffness measured 70 RDC units, representing a 7 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. Zo Sweet added 14 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 6.0. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. Playtesters were instructed to install the poly (white string) in the mains and the nylon (natural string) in the crosses, and that the string was to be installed at normal tension. Average number of hours playtested was 22.9.

Most of our playtesters told us that Zo Sweet is as easy to string as other strings, with the rest just about evenly split as to whether they found it easier or more difficult than normal. For some reason, the Zo Power mains feel much thicker than the TNT² crosses, even though it is thinner. Being polyester, the Zo Power mains are stiff, but not difficult to install, and it knots up nicely. Installing the TNT² crosses is wonderful. The string is soft and pliable, so it weaves around the mains easily, and the ends don’t mush out, so blocked holes are no problem. It’s also convenient that the tension can be set the same for the Zo Power and the TNT², as it’s one less thing to deal with.

One playtester broke his sample during stringing, four reported problems with coil memory, two reported problems tying knots, and none reported friction burn.

On the court

According to our playtesters, Zo Sweet 17 is a solid all-around performer, scoring well above average in Playability, Durability, Power, Control, Spin Potential, Tension Holding, and Resistance to Movement. These scores include three top-ten finishes for Zo Sweet out of the 96 strings we’ve playtested to date (in Durability, Spin Potential, and Tension Retention). Not surprisingly, the overall score is also well above average.

Four samples broke during play, one each at four hours, six hours, 10 hours, and 20.5 hours.


Clearly, not every member of our playtest team falls into the category of “intermediate to advanced players with fast swing speeds,” although you’d hardly know it from the overall scores they awarded Gamma Zo Sweet. The scores probably have more to do with increasingly better string technology, which offers such a wide range of performance that even less advanced players can appreciate the characteristics.

Hybrid strings do make it easier to experiment with differences in tension between the mains and crosses, but strictly from a stringing point of view, it’s nice that a durable hybrid such as Zo Sweet allows you to use the same tension throughout, even though the mains are polyester and the crosses are nylon.


“For a hybrid, it really surprised me. I love how much spin I can get and how long it lasts. It isn’t hard on my elbow like some other stiffer hybrids. I’d definitely recommend it to tournament players. I’ll switch to it myself.” 5.5 male baseliner with heavy spin using Prince AirStick OS strung at 56 pounds LO (Wilson Sensation NXT 16)

“I played in a 4.5 tournament and loved the playability and feel of this string. I would string it two pounds lighter. The string is still in the racquet, and still plays good after 40 hours.” 4.5 male baseliner with heavy spin using Wilson Hyper Hammer 5.2 strung at 62/59 pounds CP (Gamma 18)

“Really good string. Can’t wait to find out what it is!” 4.5 male all court player using Head Radical Trisys 260 strung at 64 pounds LO (Gamma Advantage 15L)

“Plays exceptionally well overall. I am very impressed with the comfort and overall playability. The comfort and feel aren’t as good as my normal string, but not bad at all. If I were looking for a durable and good-playing hybrid, this would be it!” 6.0 male all court player using Wilson nTour strung at 58 pounds CP (Wilson NXT 17)

“Great string for playing and teaching. This string is surprisingly comfortable with good pop. The durability is incredible, especially with the 18x20 pattern in my racquet, and it holds its tension very well for a polyester string.” 5.0 male all court player using Wilson nPS 95 strung at 61 pounds LO (Wilson Reaction 17)

“Nice surprise! Not what I expected. Feel isn’t on par with my normal hybrid, but this is rather good. I’d give it a second try.” 5.0 male baseliner with moderate spin using Head Liquidmetal Prestige strung at 54 pounds CP (Luxilon/VS hybrid 17)

“Great durability, not bad playability.” 5.0 male all court player using Prince O3 Red strung at 68.5 pounds CP (Babolat Touch 16)

“The string seems to be a 17-gauge, but is more durable than my normal 16 gauge. Even though it is thinner, it is not more lively, which I like. It seems to have poly mains, and I think it is easier to work with than other polys in hybrid sets.” 5.5 male all court player using Dunlop 200G strung at 62 pounds CP (Wilson Sensation 16)

“This string has quite a nice feel with no harshness. It is more powerful and springy than I would have suspected. The crosses handled quite well and seemed to hold up quite well. Only minor complaint is the string movement, but the racquet has a very wide pattern (14x18) so this is almost expected. I would use this string if it is at a good price point and the durability keeps up.” 4.0 male all court player using Tecnifibre T Feel 290 XL strung at 60 pounds CP (Klip Excellerator 17)

“This string is quite easy to install. Very good-feeling string for a hybrid. Very durable. After about 50 hours of use I started to see movement. After 100 hours of playing and teaching, it still feels good.” 5.0 male all court player using Head i.prestige mid strung at 58 pounds LO (Head Ultratour 17)

“A reasonable alternative for those players who like a softer, more playable string that is somewhat more durable with good resistance to string movement.” 3.5 male all court player using Prince Triple Threat Graphite strung at 65 pounds LO (Forten Ultra Thin Blend 18)

“I’m very pleased with this string. I’d purchase it for my other racquets. I sometimes get as few as five minutes out of a set of string, and this one’s still going after 15 hours.” 5.0 female baseliner with heavy spin using Volkl C10 Pro Tour strung at 65 pounds LO (Gamma 16)

“I do not tend to break strings, though I hit fairly hard, and I also serve hard. I like this string a lot. It’s durability is difficult to gauge on a breakage level, but after 35 hours there’s still life in them.” 3.5 male all court player using Yonex RD-27 strung at 55 pounds CP (Kirschbaum 16)

“This string is a good alternative to any all-polyester string. The extremely soft crosses add playability, while the poly mains offer control and spin potential.” 4.0 male all court player using Yonex RDX-500 strung at 65 pounds LO (Gamma TNT2 17)

“Excellent playability. Surprisingly good feel. Spin potential is okay, but I can compensate by changing my racquet head speed. The strings tend to move a bit. Overall, a decent string.” 5.0 male all court player using Head S.12 strung at 56 pounds LO (Wilson NXT 16)

“When I opened the demo package, I realized this was going to be another one of those attempts to mask the stiff play of monofilament mains with soft cross strings, but I was pleasantly surprised. Once you get over the stiff stringing of the mains and some difficulty pushing the soft crosses through a few shared holes, the playing really made up for everything. This string holds its tension pretty well, gives a really true hit, and isn’t that hard on the wrist. Though it lacks a bit in power, it makes up for it with good control. This hybrid is one that I would recommend to my customers.” 4.5 male all court player using Fischer GDS Rally FT strung at 62 pounds LO (Wilson Sensation 16)

“Nice playing string! Not nearly as stiff as lots of hybrids are. Good power potential with no loss of control. I would stock this string in my shop!” 5.0 male all court player using Wilson nTour strung at 57 pounds CP (Wilson Stamina Spin 16)

“Very impressed with this string from the beginning, compares very favorably with my usual hybrid combination, in fact the crosses are holding up better than expected. Strings settled in quickly with good crispness, power and touch, minimal loss of tension despite lots of hard play and warm weather. Would be happy to recommend these strings for all conditions.” 5.0 male baseliner with moderate spin using Head Ti 6 strung at 61 pounds LO (Luxilon Big Banger/Tecnifibre 515 Gold 16)

“The feel of the string was wonderful right out of the gate, but tapered off after five hours of play. This string moved more than most polyesters I’ve used.” 5.0 male all court player using Prince Tour Diablo strung at 66 pounds CP (Unique Tourna Poly 18)

“This hybrid feels somewhat better than other similar hybrids. It has good control but does tend to lose tension quickly.” 5.0 male all court player using Babolat Pure Drive strung at 58 pounds CP (Tecnifibre E-Matrix 17)

“The durability of the string is great, but I’m not happy with its hardness.” 3.5 male all court player using Wilson nSix-One 95 strung at 57 pounds LO (Gamma Synthetic Gut 16)

“I like the overall playability of this string, but the crosses seemed to fray quickly.” 3.5 male all court player using Wilson nSix-One 95 strung at 66 pounds LO (Prince Synthetic Gut w/Duraflex 16)

“This strung up tighter than my regular string. Seemed too powerful at first. It’s also quieter than my all-poly strings. Good string, though.” 5.0 male all court player using Wilson H Rival strung at 57 pounds CP (Wilson Enduro Pro 16)

“I’ve experimented with poly hybrids in the past, and the crosses in this one seem relatively soft. I think this gives it a bit more feel.” 4.5 male all court player using Babolat Pure Control MP strung at 55 pounds CP (Klip Scorcher 17)

“Normally I do not like hybrids. However, this one plays better than I anticipated. Very good control, and adequate power.” 4.0 male baseliner with moderate spin using Pro Kennex Core 1 #6 strung at 60 pounds CP (Gamma TNT 18)

“The cross strings softened up the string bed more than I thought they would. Did not offer the power or control I am looking for.” 4.0 male all court player using Fischer Pro. No. One strung at 64 pounds CP (Gamma XP 17)

“Good string. I didn’t have real good feel with it.” 3.5 male all court player using Dunlop M-Fil 3 Hundred strung at 55 pounds LO (Klip Natural Gut 16)

“More than enough string length. This string is not going to cut it for the touch player or instructor. It generally plays very boardy, with very little feel or control even after several hours of play. A most disappointing product. I would not recommend it to my customers.” 3.5 male all court player using Wilson Hyper Pro Staff Surge 5.1 strung at 58 pounds CP (Tecnifibre 515 Gold 17)

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


(compared to other strings)
Number of testers who said it was:
much easier 1
somewhat easier 6
about as easy 21
not quite as easy 5
not nearly as easy 0
(compared to string played most often)
Number of testers who said it was:
much better 3
somewhat better 6
about as playable 10
not quite as playable 10
not nearly as playable 4
(compared to other strings of similar gauge)
Number of testers who said it was:
much better 9
somewhat better 10
about as durable 12
not quite as durable 1
not nearly as durable 0
From 1 to 5 (best)
Playability 3.5
Durability 4.3
Power 3.5
Control 3.6
Comfort 3.2
Touch/Feel 3.1
Spin Potential 3.5
Holding Tension 3.6
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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