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Playtest: Wilson Hollow Core Pro

By Greg Raven

Hollow Core Pro is an innovative nylon and polyester multifilament from Wilson. Instead of a round solid core, Hollow Core Pro has an air-filled, hollow triangle-shaped polyester core. According to Wilson, this hollow core is what gives the string its unique playing properties. The hollow core lends exceptional shock absorption, and the triangular shape of the core gives the string added strength. Around the triangular core are wrapped high-elasticity microfibers of nylon and fluorocarbon for increased performance and comfort. Hollow Core Pro is coated for ease of installation.

We published a playtest of Hollow Core 16 in the April 2009 issue of Racquet Sports Industry magazine. The Hollow Core Pro used in this test has a thinner diameter for added “bite” and spin.

Wilson tells us that Hollow Core Pro is for players looking for a string that provides exceptional ball touch and feel. This string will suit players who like a crisp feeling string that provides superb control and feel on all shots.

Hollow Core Pro is available in 17 only in gold only. It is priced from $11.25 for sets of 40 feet, $162.50 for reels of 660 feet. For more information or to order, contact Wilson at 773-714-6400, or visit wilson.com/newstring.

In the lab

The coil measured 40 feet. The diameter measured 1.26-1.28 mm before stringing, and 1.23-124 mm after stringing. We recorded a stringbed stiffness of 78 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), stringbed stiffness measured 71 RDC units, representing a 9 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. Wilson Hollow Core Pro has a stiffness of 180 and a tension loss 16.95 pounds. Hollow Core Pro added 13 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 21.1.

Hollow Core Pro presented no problems during stringing.

No playtester broke his sample during stringing, none reported problems with coil memory or tying knots, and one reported friction burn.

On the court

Wilson Hollow Core Pro posted some good numbers, including well-above-average ratings in Control, Comfort, Playability, Tension Retention, and Touch/Feel. As good as these numbers are, though, they pale compared to the glowing comments our playtesters gave Hollow Core Pro. There’s a sample of the comments at the end of this report, but if you read the full text of the comments on-line, you’ll see that our playtest team said very nice things about every aspect of Hollow Core Pro. Hollow Core Pro garnered an above average overall rating of the 141 strings we’ve playtested for publication.

Eight playtesters broke the sample during the playtest period, one each at 3, 5, 6, 7, 8, 10, 12, and 20 hours.

Conclusion

In a world that seems to be becoming swamped in polyester strings, a soft, thin, easy-to-install nylon can be a real treat. Hollow Core Pro offers many of the same benefits as Hollow Core 16, although it is a bit more of a niche string, if for no other reason than it is a thinner gauge.

Playtester comments

“This string gets better with age. It plays like natural gut. The spin and feel are exceptional. I would definitely buy this string.” 6.0 male all-court player using Wilson K Tour strung at 57 pounds CP (Wilson NXT 17)

“Pre-stretching makes this string more manageable during the installation process. The comfort and power are noticeable from the first hit. Controlling trajectory and distance on soft touch shots is a cinch.” 4.5 male baseliner with heavy spin using Head i.Radical OS strung at 66 pounds CP (Luxilon Ace 18)

“This is a very comfortable string with outstanding feel.” 5.0 male all-court player using Prince OZone Seven strung at 60 pounds CP (Prince Lightning XX 16)

“Great tension maintenance. Very crisp response without any harsh feedback. This would make the perfect hybrid cross.” 5.5 male all-court player using Tecnifibre T Fight 320 VO2 Max strung at 65 pounds LO (Tecnifibre Black Code/Tecnifibre X One Biphase 16/16)

“This string has a gut-like feel with exceptional playability. Outstanding comfort and control.” 5.0 male all-court player using Prince Triple Threat Warrior MP strung at 58 pounds CP (Signum Pro Poly Plasma 17)

“Excellent control, playability, and spin. Durability is no slouch either.” 5.5 female all-court player using Babolat Drive Z Lite strung at 60 pounds CP (Babolat Xcel Premium 16)

“Great all-around string with impressive durability and resistance to movement.” 4.0 male baseliner with moderate spin using Yonex RQIS 2 Tour strung at 54 pounds CP (Prince Poly EXP 17)

“Perfect mix of comfort and control. Great feel. Compares favorably to the best multifilaments on the market.” 5.5 male all-court player using Prince EXO3 Rebel (hole inserts) strung at 59 pounds CP (Luxilon Alu Power/Wilson NXT 16L/16)

“This string has all the trappings of quality product. Very predictable response. Hitting a heavy, surgically placed ball is almost effortless. The feedback is excellent. I would definitely recommend this string.” 4.5 male serve-and-volley player using Wilson K Three strung at 60 pounds LO (Gamma Zo Sweet 17)

“Superior comfort, control, and tension maintenance. Nice crisp response. Great feel.” 4.5 male serve-and-volley player using Babolat Pure Drive strung at 61 pounds CP (Wilson NXT 16)

“The string has a great combination of durability and playability. While not a soft string, it does have great feel and touch. It has the responsiveness of a top notch multifilament.” 5.0 male serve-and-volley player using Prince EXO3 Red strung at 61 pounds LO (Prince Premier LT 17)

“Great feel, touch, power, and comfort. The high dwell time imparts a sense of control. I may have to change strings!” 5.0 male all-court player using Wilson K Six One (76 holes) strung at 58 pounds LO (Wilson Ultimate Duo 16)

“This a comfortable string with remarkable control. Even on my worst strokes, I never get the sense of spraying the ball. There is zero trampoline effect, enabling high head speed and aggressive targeting.” 4.0 male all-court player using Wilson K Pro Tour strung at 58 pounds CP (Wilson Sensation 16)

“After ten minutes this string felt like an old friend. Great comfort, power, spin, and control.” 4.5 male baseliner with moderate spin using Head MicroGEL Prestige Mid Plus strung at 58 pounds LO (Head Sonic Pro 17)

“High playability for a durability string. The tension maintenance is surprisingly good. The sticky surface helps to limit string movement. Great feel.” 5.0 male all-court player using Head i.Speed MP strung at 60 pounds CP (Prince Lightning XX 16)

“I have never had much luck with nylon multifilaments. This string is an exception to the rule. Not only does it have the usual comfort benefits that come with a softer string, but the string bed is not too springy or mushy. The manufacturer has definitely figured something out.” 5.0 male all-court player using Volkl DNX 10 Midplus strung at 62 pounds CP (Luxilon Alu Power Rough 16L)

“Three words: control, power, comfort. String breakers are advised to hybrid this. It would definitely complement many of the stiffer polyesters.” 4.5 female all-court player using Head YOUTEK Radical MP strung at 60 pounds LO (Babolat Pro Hurricane Tour/Nylon Multifilament 17/16)

“This string is comfortable with a great feel. It starts to move after a few hours. Tension maintenance is on the low side.” 4.5 male all-court player using Wilson K Four strung at 60 pounds CP (Luxilon Alu Power Rough 16L)

“This string grips the ball. The bite is excellent. It has great touch. String movement is fairly high.” 4.0 male all-court player using Tecnifibre T Fight 335 (18x20) strung at 60 pounds CP (Isospeed Baseline Control/Gamma TNT2 16/16)

“This string has a very rare combination of comfort, power, and control. It is at once soft without being mushy, and firm without being harsh.” 5.0 male all-court player using Wilson K Blade strung at 55 pounds LO (Babolat Hurricane/Wilson Sensation 17/16)

“This string has a stiff feel with excellent spin and control.” 4.5 male all-court player using Prince EXO3 Rebel (hole inserts) strung at 57/60 pounds CP (Prince Synthetic Gut w/Duraflex 16)

“This plays as well as some of the top multifilaments on the market. The comfort and power truly stand out. I would prefer more bite in order to control the power.” 4.5 male all-court player using Volkl C10 Pro strung at 60 pounds LO (Tecnifibre Black Code 18)

“This is a very comfortable string with the right mix of power and control.” 4.0 male all-court player using Head MicroGEL Radical MP strung at 57 pounds LO (Gamma Live Wire XP 17)

“Pinpoint control on serves and volleys. The depth control makes this a volleyers dream. No vibration at impact. Very little bite.” 6.0 male all-court player using Wilson nBlade strung at 54 pounds CP (Wilson Sensation 16)

“Great tension maintenance and resistance to movement. As a natural gut user, I found the playability and comfort to be on the low side.” 4.0 male all-court player using Fischer Pro No. One FT strung at 58 pounds LO (Wilson Natural 16)

“Very easy installation. This string performs great ‘out of the box.’ Excellent comfort and touch. After nine hours the string starts to fray and the playability goes down. Big hitters and string breakers might need something a little more durable.” 4.5 male all-court player using Prince O3 Blue strung at 55 pounds LO (Gamma Live Wire 17)

“This string has a crisp yet comfortable response. Above average control and spin. The strings start to move after about two hours. This is recommended to players who want the best of both worlds: a stiff response with a comfortable feel.” 4.5 male all-court player using Wilson K Pro Open strung at 60 pounds LO (Gosen Polylon/Babolat Conquest 17/17)

“Great feel. Very predictable response. Slight notching after six hours. Multifilament fans looking for a stiffer, more controlled response should give this a try.” 4.0 male baseliner with moderate spin using Head Metallix 2 strung at 56 pounds CP (Wilson NXT 16)

“The sticky coating causes some burning during installation. This string has a very powerful sweet spot. It also seems to ‘grab’ the ball, which adds to the control. Notching occurs early.” 3.5 male all-court player using Volkl Power Bridge 4 strung at 56 pounds CP (Wilson K Gut Pro 16)

“Plays like a high end multifilament. It has a wonderfully soft and somewhat muted response. Predictably low durability.” 4.5 male all-court player using Volkl DNX 1 w/Power Arm strung at 56/54 pounds CP (Forten Dynamix 16)

“High playability, low durability. Topspin players with loose patterns might want to consider string savers.” 4.5 male all-court player using Prince O3 Speedport Black (port inserts) strung at 52 pounds CP (Luxilon Ace/Pro Supex Maxim Touch 16/17)

“Very easy installation. String movement, fraying, and notching happen inside of ten hours. The playability is average and the power is low.” 5.0 male baseliner with heavy spin using Volkl Boris Becker 10 strung at 60 pounds CP (Gamma Synthetic Gut 16)

“This is a very elastic string which notches slightly after a few hours of play.” 4.0 male baseliner with moderate spin using Prince O3 Speedport Pro White strung at 62 pounds CP (Forten Pro Select 18)

“String movement, tension loss, and durability are problematic. Playability is not bad.” 4.5 male all-court player using Babolat Pure Drive GT strung at 59 pounds CP (Gosen Polylon 17)

“Topspin players take note: the crosses move and fray pretty easily.” 4.5 male baseliner with moderate spin using Wilson nPro strung at 63 pounds LO (Wilson Sensation 16)

“This string felt awful. It has no power, playability, or feel. However, tension maintenance is decent, and string movement is low.” 4.0 male all-court player using Prince EXO3 Graphite (port inserts) strung at 58 pounds CP (Luxilon Alu Power Rough 16L)

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

Playtester ratings

EASE OF STRINGING (compared to other strings)
Number of testers who said it was:
much easier	6
somewhat easier	11
about as easy	19
not quite as easy	0
not nearly as easy	0
OVERALL PLAYABILITY (compared to string played most often)
Number of testers who said it was:
much better	1
somewhat better	9
about as playable	12
not quite as playable	14
not nearly as playable	0
OVERALL DURABILITY (compared to other strings of similar gauge)
Number of testers who said it was:
much better	1
somewhat better	7
about as durable	13
not quite as durable	11
not nearly as durable	4
RATING AVERAGES From 1 to 5 (best)
Playability	3.4
Durability	2.8
Power	3.3
Control	3.6
Comfort	3.5
Touch/Feel	3.3
Spin Potential	3.1
Holding Tension	3.4
Resistance to Movement	2.8

See all articles by Greg Raven

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 greg@usrsa.com, or through Facebook, LinkedIn, and Twitter. He plays tennis three to five days a week, and is turning into an avid cyclist.

From the May 2010 issue
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