Tennis Industry magazine


String Playtest: Pacific Poly Force Black Series 1.20

By Greg Raven

Pacific Poly Force is a monofilament “poly,” which is to say that while many would classify it as being in the polyester family, it is not truly polyester-based. Pacific tells us that Poly Force is strong and powerful while providing maximum control, and that it features the Long Term Elasticity system (LTE), which provides long-lasting energy and playability.

Poly Force Black Series is available in 1.29 mm (16L) and 1.24 mm (17) in orange or black, and 1.20 (18) in black only. It is priced from $12 for 40-foot sets and $155 for 660-foot reels. For more information or to order, contact Pacific at 941-795-1789 or, or visit Poly Force is 100 percent manufactured in Pacific’s factory in Germany, as have all Pacific polyester strings since 1972.

In the Lab

We tested the 1.20-mm (18-gauge) Poly Force Black Series. The coil measured 40 feet, 3 inches. The diameter measured 1.20 mm prior to stringing and 1.18 mm after stringing. We recorded a string-bed stiffness of 70 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), string-bed stiffness measured 66 RDC units, representing a 6 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 had a stiffness of 217 and a tension loss of 11.67 pounds, while Pacific Poly Force Black Series 1.20 had a stiffness of 178 and a tension loss of 21.65 pounds. Poly Force Black Series 1.20 added 14.9 grams to the weight of our unstrung frame.

The string was tested for five weeks by 33 USRSA playtesters, with NTRP ratings ranging from 3.5 to 6.0. These were blind tests, with playtesters receiving unmarked strings in unmarked packages. Average number of hours playtested was 22.2.

Working with Poly Force Black Series was much like working with a polyester string. Out of the package, it felt thicker than an 18, as noted some playtesters. It felt as though it had some sort of coating on it, which we wiped off before stringing.

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

On the Court

Our playtesters loved the Spin Potential of Pacific Poly Force Black Series 1.20, giving it an excellent rating. They also enjoyed its Durability, Resistance to Movement, Control, and Playability, with ratings well above average in each of these categories. These scores were more than enough to give Pacific Poly Force Black Series 1.20 an overall rating that is well above average.

No playtester reported premature fraying or peeling, one reported buzzing and nine reported notching. Four playtesters broke the sample during play, one each at 13, 18, 25 and 55 hours.


With ratings such as these and three gauges from which to choose, Poly Force Black Series seems to be a solid offering, no matter what it’s made of.

In particular, Poly Force Black Series’ results in the Spin Potential category speak for themselves, and when you factor in the ease of working with the string (it has a cylindrical shape, unlike the many geometrically shaped strings that also rate highly in Spin Potential), you can offer your customers a spin-friendly string that you won’t hate to install. — Greg Raven

Playtester Comments

“I loved this test string! If this string were available now I would most definitely switch to it! Stringing was much easier as the string barely had any coil memory. It didn’t have very much friction at all while stringing either. Playing-wise, what stuck out the most, was how comfortable the string felt without losing the feeling of a firm string bed.” 5.0 male all court player using Yonex VCore Si strung at 54 pounds CP (Head Hawk 17)

“I was impressed with the playability and feel of this string, especially since I normally use what I believe to be a much thinner gauge poly string.” 4.0 male all court player using Head Prestige PWR strung at 50 pounds CP (Gamma iO 18)

“High-end polyester string featuring exceptional overall playability, control, and durability. You can really feel the pop of a hard flat serve as well as the heavy spin of a topspin roll shot. The string had great tension maintenance and snapped back into position after shots until the string broke after 55 hours of teaching and playing. A+.” 4.5 male all court player using Wilson Steam strung at 54 pounds CP (Luxilon 4G Rough 16L)

“These strings felt a little stiff when I initially hit with them. Over time they ‘broke in’ and felt really good. These strings are more suited for the power player who hits out and hits with heavy top spin. I would definitely purchase these strings.” 5.5 male all court player using Babolat Pure Drive strung at 54 pounds CP (Babolat VS 16)

“Great spin and power with this string! More power than the majority of polyester strings I have used. As a fan of thinner strings, this one was a winner for me. This string is a spin machine! Durability was lacking compared to my usual string, but that is to be expected with this gauge of string. I would easily compromise durability for the extra spin and power that this string provides!” 5.0 male baseliner with heavy spin using Wilson BLX Pro Open strung at 58 pounds LO (Luxilon ALU Power 1.25)

“I really like this sample. It plays every bit as good as my usual string yet it feels softer. I had good control, great power and the sample is a very comfortable string. I was able to get good bite on the ball and the string feel was very good. This string is good for my racquet and good for my game.” 4.5 male serve-and-volley player using Head Graphen XT Instinct strung at 50/52 pounds CP (Tecnifibre Black code/Head Velociti MLT 18/16)

“This string played really well and is a great poly! I enjoyed the control on my shots! Recommended for synthetic gut string breakers who are looking for more control and durability. Current poly players should give it a try too!” 3.5 male baseliner with heavy spin using Babolat Pure Drive Roddick strung at 56 pounds LO (Solinco Tour Bite 16L)

“This string had great feel and I found it easy on the arm. I would recommend not to reduce the tension by the 10 percent rule because of the playability of this string is so good. For serve and volley players it may be OK, but for baseline players higher tension would give you more control and spin potential. This is perfect for recreational players who would want to use a poly but get the feel of a multifilament string.” 4.5 male serve-and-volley player using Head Radical MP strung at 53 pounds CP (Luxilon ALU Power Feel 18)

“I absolutely loved this string! I’ve used a lot of polyesters and this is one of the best. I’m hitting the best groundstrokes of my life, with the bite the string gives me. I’m switching to it.” 5.0 male all court player using Babolat Paure Drive + strung at 40 pounds LO (Babolat RPM Blast 16)

“Really enjoyed teaching with this string. I would be open to trying it out on a few of my quality junior players!” 4.0 male all court player using Babolat Pure Drive strung at 60 pounds CP (Luxilon Original 16)

“The string exhibited good power. The topspin was better than average. The tension loss over the three weeks it was in my frame was about seven pounds. Overall the string performed well with regards to playability.” 4.5 male all court player using Head YouTek Four Star strung at 54/54 pounds LO (Luxilon Original/Prince Syn. Gut with Duraflex 17/16)

“This string had great touch and feel. This string in a hybrid either way would be excellent. I was able to place my serve wherever I wanted to.” 4.5 male all court player using Babolat Pure COntrol strung at 52/50 pounds LO (Babolat RPM Blast 15)

“With very good control and a very comfortable feel, this string was a pleasure to play with, although I wish it had a little more power. Spin control was good, but didn’t add any extra jump to my topspin or kick serve. Didn’t improve my game any, but would highly recommend to someone looking for a durable, comfortable poly that is easy on the arm.” 4.5 male baseliner with heavy spin using Babolat Pure Drive Tour Plus strung at 52/52 pounds CP (Babolat Tonic/Yonex Poly Pro Tour 15L/16)

“This was a very comfortable monofilament string. I am not sure if there was some coating on the outside, but the string felt easier to install than other polyester monofilaments. I did like the ball pocketing and was pleasantly surprised at the amount of control and comfort for a monofilament. I would definitely recommend this for someone who wants to play with monofilament but wants one that is easier on the arm.” 4.0 male all court player using Wilson Blade S strung at 42/42 pounds CP (Solinco Tour Bite Soft/Babolat nvy 16L/17)

“This sample and I became good friends. Excellent string. Covered all the bases well. I would consider using it. One interesting point was that I found that it took a few sessions to really break it in nicely which is pretty unusual for a poly or a co-poly. Had surprisingly good touch and feel on the compact shots: Volleys, drop shots, and tactical underspin forehands.” 5.0 male all court player using Wilson Juice 100S strung at 54/54 pounds LO (Babolat RPM Blast/Wilson Sensation 17/16)

“Good above-average string. I would recommend lowering more than was suggested to match feel of your normal string. Tension maintenance was excellent and the strings stayed put. I would recommend for any hard-hitting baseliner.” 6.0 male all court player using Wilson Blade (16x19) strung at 45 pounds CP (Wilson NXT 16)

“String played very well. Good spin and power potential.” 4.5 male all court player using Yonex VCore F97 strung at 51 pounds CP (Prince Synthetic Gut 16)

“The string generated a really good bite on the ball and generated a lot of spin. The test string was 16g but my preference is 17 gauge so I didn’t quite have the feel on certain shots.” 4.0 male all court player using Babolat Pure Aero Team strung at 55 pounds CP (Solinco Tour Bite Soft 17)

“The test string is a very firm playing poly string. I should have strung it at 47-49 pounds. The strings main characteristic is terrific tension maintenance and very durable. This string will make a excellent main string in a hybrid pattern for frames 110 square inches or larger.” 3.5 male baseliner with moderate spin using Prince Speedport Black strung at 52/52 pounds CP (MSV Hex/Solinco Tour Bite 19/20)

“Fairly stiff string, good for spin and doesn’t move. Solid feel but not much power. Easy to hit the serve in the box.” 4.5 male all court player using Head Speed strung at 52 pounds CP (Solinco Hyper G 16L)

“The string played well for the first few hours, but as the playtest continued, it lost significant tension, power, spin, and feel.” 4.0 male baseliner with heavy spin using Prince Response strung at 48/48 pounds CP (Babolat VS/Luxilon Element 16/16)

“At 48 pounds, the string provided more power than expected. I could have strung it a couple of pounds higher. I found the comfort to be nice for full poly, but the tension dropped significantly after about 6 hours of hitting.” 4.5 male all court player using Prince Textreme Tour strung at 48/48 pounds CP (Prince Tour XC/Prince Premier Control 16L/16)

“I strung two new rackets at the same time, one with the test string, one with Head Sonic Pro 17. The Sonic Pro started with a DT of 41, and the test string’s DT was 39. After about 20 hours of play with each, the DT went down 8 on each, 33 and 31. The test string seemed slightly easier to string, as it was a little slicker with less coil memory, and it seemed a little thinner than the Sonic Pro. During play, I really did not notice a difference between these two strings, which was surprising, as I am usually very aware of minute differences.” 4.5 male baseliner with heavy spin using Head Graphene XT Prestige strung at 50 pounds CP (Head Sonic Pro 17)

“The string was very comfortable; however this string lost tension quickly.” 4.0 male baseliner with moderate spin using Wilson Steam strung at 58 pounds CP (Tourna Big Hitter Black 17)

“Seemed like a typical poly string. Lots of power, sometimes too much. Was OK from the baseline but I didn’t have the best feel at the net.” 4.0 male all court player using Wilson Steam 105S strung at 60/60 pounds CP (Luxilon ALU Power/Gamma TNT2 1.25/16)

“Didn’t care for this string. Certainly a passable polyester, but not as much touch, spin, or power as other polyesters I have used or tested. It did seem to hold tension well and was durable. I would recommend it to a frequent string breaker who doesn’t need spin or power.” 4.5 male baseliner with moderate spin using Head YouTek Speed S strung at 46 pounds CP (Tourna Big Hitter Black 7 16)

“A middle of the road string, pretty much average in all categories. I think price would be a determining factor as to whether or not I would stock this string.” 4.0 male baseliner with moderate spin using Yonex EZone Team + strung at 45 pounds CP (Wilson Sensation 16)

“Nothing special about this string. Sort of an average poly string. This string was durable as most poly strings are. The control was very good even at the lower tension of 46 pounds. It may be a good hybrid candidate as a cross string.” 3.5 male all court player using Dunlop iDapt strung at 46/46 pounds CP (Prince Premier Power/Prince Syn. Gut 17/18)

“The first couple of matches I played, I really liked the string’s power and playability. There was absolutely no string movement in the bed. However, after four sets of tennis there was a noticeable loss in tension. Control became very difficult as the tension continued to drop. The string broke after ten sets of tennis, which was approximately 13 hours of play. There was still no string movement. I wished I had strung a bit tighter initially.” 4.0 male all court player using Babolat Aero Pro Drive GT strung at 54 pounds LO (Tourn Quasi-Gut 16)

“In the thick forest of poly strings now available this string was just another standing tree. I found this string to be non-forgiving and had a harsh feel on impact. For hard hitters this string may have some potential, but I would not recommend it for the average player” 4.5 male all court player using Head Instinct MP strung at 50 pounds CP (Solinco Hyper G 17)

“I did not like this string, mostly from a playing perspective. It strung up easily but lost 14.0% before playtesting (reference tension = 53 pounds, Stringmeter reading before play = 45.6 pounds). It was very stable but played much softer in 75-degree weather than at 45 degrees. It displayed low spin potential and low power in spite of its thin gauge and low reference tension. I hit as hard as I could with few balls sailing out. This would be a good choice for a hard baseliner but lacked finesse. It displayed excellent resistance to movement and tension maintenance once strung (Stringmeter reading after 16 hours = 43.7% — only 3.5% additional loss vs. reference tension — or 4.2% vs. unplayed tension). Considerable notching of mains was observed.” 4.5 male all court player using Wilson Juice 100S strung at 53/53 pounds CP (Tecnifibre Red Code/Gamma Synthetic Gut 18/16)

“These strings did not impress me. I did not find anything special like increased spin, extra ball pocketing, additional feel, or extra power. Besides having good control it felt like using a board. I was hoping for that extra pop or additional spin but it never came through for me. I keep my hopes up for that diamond in the rough, the Excalibur of strings!” 4.5 male all court player using Pro Kennex Kinetic Pro 7g strung at 54 pounds CP (Luxilon ALU Power 1.25)

“I really disliked it at first. It got somewhat better with time. No ‘feel’ with this string. It might be fine in a hybrid, but I didn’t care for it in a full bed.” 3.5 male all court player using Wilson Blade strung at 50/50 pounds CP (Solinco Tour Bite/Tecnifibre NRG2 17/17)

Playtester Ratings

Ease of Stringing (compared to other strings)

Much easier: 2

Somewhat easier: 3

About as easy: 19

Not quite as easy: 9

Not nearly as easy: 0

Overall Playability (compared to the string played most often)

Much better: 1

Somewhat better: 8

About as playable: 5

Not quite as playable: 15

Not nearly as playable: 3

Overall Durability (compared to other strings of similar gauge)

Much better: 2

Somewhat better: 10

About as durable: 18

Not quite as durable: 3

Not nearly as durable: 0

Rating Averages from 1 to 5 (best)

Playability: 3.5

Durability: 3.9

Power: 3.3

Control: 3.6

Comfort: 3.1

Touch/Feel: 3

Spin Potential: 3.6

Holding Tension: 3.2

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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