Hollow Core Pro Harnesses the Power of Air

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.

Wilson Hollow Core Pro

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.

Wilson Hollow Core Pro cross-section

Hollow Core Pro is available in 17 only in gold. 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.


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.

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