Tennis Industry magazine


Playtest: Volkl F.I.R.E. Strings

By Greg Raven

Volkl F.I.R.E. String Volkl’s F.I.R.E. (Fully Integrated Racquet Engineering) Strings is a hybrid comprised of a nylon multifilament and polyester monofilament. According to Volkl, this combination delivers the power and feel of a multifilament with the durability and control of the polyester. The interaction of these two string types was specially developed to support Volkl’s Catapult racquets: The elasticity of the multifilament enhances the Catapult power, while the stiffer polyester increases durability and enhances the resetting of the string bed through the Catapult springs.

Volkl points out that F.I.R.E. Stringsenables easy “tuning” of your racquet to your liking: For maximum power, use the multi-filament (yellow and black string) in the mains, and the polyester (white) in the crosses.For maximum control and durability, use the polyester in the main strings, and the multi-filament in the crosses.

Volkl recommends F.I.R.E. Strings for players who seek the high-performance associated with natural gut, but want more dependable control and greater durability.

F.I.R.E. Strings is available in 16L/17L in yellow/black and white. It is priced from $12.00 for sets of 20 × 2 feet, and $160.00 for reels of 360 × 2 feet. For more information or to order, contact Volkl at 800-264-4579, or visit

In the Lab

We tested the 16L/17L gauge F.I.R.E. Strings, using the multifilament in the mains and the poly in the crosses. The coils measured 22’8” for the mains and 23’ for the crosses. The diameters measured 1.38-1.39 mm (mains) and 1.28-1.30 mm (crosses) prior to stringing, and 1.32 mm (mains) and 1.25 mm (crosses) after stringing. F.I.R.E. mains recorded a single-string stiffness of 175 lbs/in., and a tension loss of 9.5 pounds. F.I.R.E. crosses recorded a single-string stiffness of 258 lb/in., and a tension loss of 12.8 pounds.

We recorded a stringbed stiffness of 68 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 62 RDC units, representing a 9% 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% tension loss. F.I.R.E. added 14 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 6.5. These are blind tests, with playtesters receiving unmarked strings in unmarked packages. Average number of hours playtested was 20.8.

It seemed odd to put the nylon in the mains, rather than putting the more durable poly there to resist breakage. Our playtesters were just about evenly split on the degree of difficult of installing F.I.R.E. Strings, but given the slightly stiff nature of the nylon and the need to weave the much stiffer poly through the nylon, we expected a much lower rating here. As stiff as it is, the tip of the nylon can become somewhat mushy on small-diameter grommets and blocked holes, making matters just that much more difficult. If you decide to try this string with the poly in the mains, however, you’ll find it easier to string.

No playtester broke his sample during stringing, eight reported problems with coil memory, five reported problems tying knots, and two reported friction burn.

On the Court

The obvious reason to use a hybrid string such as F.I.R.E. Strings is to gain durability without sacrificing all touch and feel, and according to our playtesters, F.I.R.E. Strings is durable: 23 playtesters rated it more durable than other strings of similar gauge. F.I.R.E. Strings also garnered more favorable comments than any other string we’ve tested recently, as almost two-thirds of our playtesters had something favorable to say about it.

Our playtesters weren’t just paying F.I.R.E. Stringslip service, as they rated well above average in Durability, Control, Spin Potential, Holding Tension, and Resistance to Movement — five of our nine categories! Not surprisingly, F.I.R.E. Strings’ average score is also well above average. It seems that Volkl’s F.I.R.E. Strings has something for just about everyone, especially considering the fact that you can install the other way around, with the poly in the mains and the nylon in the crosses.

The test sample broke during play for nine of our playtesters, at 5, 8, 8.5, 10, 12, 13, 14, 22, and 26 hours.


If you’re running out of options trying to get a traditional nylon or polyester string to work for you, Volkl F.I.R.E. Strings could be the way to go. With two mutually complementary string materials, you get to decide which goes in the mains and which in the crosses, and it’s a snap to use different tensions for the mains and crosses for further customization.


“I thought this was a super string. It had a great combination of playability and control, but when you throw the wonderful durability into the mix you have a super string. I didn’t love the colors, but I got over it real fast after I hit the first couple of balls. Great string!” 5.0 male all court player using Wilson Hyper Pro Staff 6.1 strung at 60 pounds CP (Luxilon Alu Power 16L)

“I absolutely loved this string and would recommend it to my clients. Other than the premature breakage, the strings were the best I have ever played with.” 4.0 male baseliner with heavy spin using Prince Triple Threat Bandit strung at 60 pounds CP (Prince Synthetic 16)

“This felt like a very good string.The nylon mains gave it a much softer feel, almost spongy. It had very good power, but lacked the touch I like in a string. I would recommend this string to players looking to give poly a chance.” 5.5 male all court player using Wilson Pro Staff Tour 95 strung at 63 pounds CP (Wilson Sensation 16)

“Fairly easy string to install. I was expecting difficulty with the poly, but not a bad install at all! String broke after 8 hours of play. Good power and control. Thought the poly would be very stiff, but the soft mains created a nice playing string that could create spin and no string movement. Overall a good solid string. Much better than I had anticipated.” 6.5 male all court player using Wilson H Tour strung at 57 pounds LO (Wilson NXT 17)

“I am predominantly a doubles player. This string really felt good on volleys. I usually hit with a lot of topspin and these strings held up well.” 3.5 male serve and volleyer using Wilson Pro Staff 6.5 strung at 60 pounds CP (Wilson Stamina 16)

“The string did a good job of stiffening the frame. It was very good in adding control. I did not feel much loss of power although it is less powerful then the string I normally use. Very little wear after 30 hours of play. There has been some drop off in power. Nice string for frequent string breakers and those who do not care about playability as much as durability.” 4.5 male baseliner with moderate spin using Pro Kennex Core 1 No. 06 strung at 59 pounds CP (Tecnifibre NRG 17)

“The mains were easy to string, but as with most poly strings, the crosses were a bit difficult to weave across the mains. There was ample string for both the crosses and mains. I really enjoyed playing with these strings as they added a lot of control to my strokes The string held its tension and there was very little movement of the mains. If someone has a power racquet that needs a little calming down, this string will help a lot. I would recommend this string to some of my power hitters looking for more control.” 4.5 male all court player using Head Liquidmetal Instinct strung at 60 pounds LO (Wilson Stamina 16)

“A very long-lasting string with average play quality. I think someone may finally have found a compromise for heavy string breakers. The first new string in awhile that I would consider carrying in my shop. Only complaint: lots of shock to the arm, but you can’t have everything.” 5.5 male all court player using Gosen Secret Carbon strung at 62 pounds LO (Gamma Live Wire XP 16)

“Hope it comes in other colors. After five hours of play it lost 20 percent of its tension. Over the next ten hours it lost five percent more. I use string with similar characteristics, so this isnormal to me. It feels the same all the time. No movement to worry about. I like this string.” 5.0 male baseliner with moderate spin using Head Liquidmetal Prestige Mid strung at 33.5 pounds LO (Head Ultratour 17)

“A nice hybrid; good feel, good pop. Not crazy about the color. Very durable.” 5.0 male all court player using Wilson H Tour strung at 55 pounds CP (Wilson Stamina Spin 16)

“Good overall string. Still in the racquet and in good shape.” 4.5 male baseliner with heavy spin using Head Ti Radical strung at 62/59 pounds CP (Luxilon Alu Power Ice 16L)

“Enjoyed the string. It feels similar to Head Intellifiber. Great color on mains. String wore very well. Very responsive; ball reacts very quickly off stringbed. String broke on an overhead: one main popped in the middle of the frame. Not too much notching. Strings stayed in position the whole time. Nice feel. Eager to find out the manufacturer and name of this string.” 5.0 male all court player using Head i.S2 strung at 55 pounds CP (Forten Kevlar Gear 16/17)

“Strung about six pounds lighter than my normal string because of previous experience with poly strings. Though the playability is not nearly as good as the gut I normally use, it was surprisingly good on sweetspot hits. The stiffness of the crosses was apparent on off center hits.” 5.0 male all court player using Prince NXGraphite MP strung at 59/56 pounds CP (Babolat gut 16)

“Had to look at directions a couple of times to verify poly on crosses. I have to admit the “bumble bee” color of mains bothered me. I was surprised by how well this string played. Good comfort and power. Not an easy combination to achieve.” 3.5 male all court player using Wilson Hyper Hammer 5.2 strung at 56 pounds CP (Gamma Live Wire XP 17)

“A good alternative for frequent string breakers. Decent playability and good control and durability. Did not play as stiff as I thought it would. Softened up after five or six hours of play. No string movement.” 4.0 male all court player using Topspin CL628 strung at 60 pounds CP (Gamma Live Wire XP 17)

“Good string breaker’s string. Tough on the eyes when strung, but strings up rather easy. Very stiff on the arm, but for a 4.5-6.0 tournament level player who is looking for durability, I would recommend it.” 5.0 male all court player using Head Liquidmetal Prestige Mid strung at 55 pounds LO (Head Ultratour 17)

“This string surprised me and I’m not quite sure what to make of it. After stringing I assumed it was a durability string, but after playing with it a while, I’m not sure how to categorize it. My arm has been bothering me, so I wasn’t excited about playing with what I thought was a durable, stiff string, lacking in power. This string played much better than I expected and did not bother my arm at all. I experienced a fair amount of tension loss, but it didn’t seem to effect the playability, indicative of a resilient string. the strings locked into place and there was almost no string movement.” 4.5 male all court player using Prince More Performance Power 1150S strung at 65 pounds CP (Prince Premier 16)

“I’m not a string breaker, so naturally there were no problems there. The string played very well and I would recommend it for those who want durability and high playability.” 3.5 male all court player using Head i.radical strung at 60 pounds CP (Kirschbaum 15L)

“I don’t like to do hybrid stringing because the mains are always too stiff and hard. This string surprised me with how good it felt. With a feel this good, and the durability of a hybrid, it should have good potential.” 4.5 male all court player using Wilson Pro Staff Torch OS strung at 63 pounds LO (Babolat Conquest 16)

“I had no major problems stringing my racquet with this string. I became concerned about kinking on the crosses, but a little extra attentiveness took care of that problem. I was surprised that the manufacturer recommended using the poly string in the crosses instead of the mains (the recommendation for my usual string). I actually felt comfortable enough to use the racquet with the new string in a match after only two hours of practice the day before. This string seemed to give me some added power without any loss of control and the spin seemed identical to my usual string. There was very little string movement during the entire time. I would have no problem changing to this string or recommending it to my customers.” 3.5 male all court player using Head Liquidmetal Radical OS strung at 58 pounds LO (Klip Blast 17)

“Good feel. Seems very durable.” 4.0 male serve and volleyer using Wilson Hyper Pro Staff 6.1 strung at 62 pounds LO (Gamma Pro Play 18)

“It held up great for a heavy hitter and didn’t break. It had plenty of coil memory, but feels better than average, and plays better than I thought it would. It took me some time to get used to it, but once I did, it was very playable and durable.” 6.0 male baseliner with moderate spin using Wilson Triad 6.0 strung at 58 pounds LO (Gamma Synthetic Gut 16)

“I liked the string a lot, but not quite as much as my normal string. If it were priced in the $8-$10 range, I would buy it. A good string overall in terms of comfort and its ability to bite the ball.” 5.5 male all court player using Prince Airstick B1025 OS strung at 59 pounds LO (Wilson Sensation NXT 16)

“Solid string, felt pretty stiff. Typical polyester, except I liked it better. Polyesters seem spongy to me. This was a more solid string and played like Kevlar, which I like. Feels really good on volleys. I would consider switching to this string. Very durable.” 5.5 male serve and volleyer using Prince More Performance Game strung at 63 pounds CP (Kevlar blend 17/16)

“Looks hot but plays lukewarm. The tiger stripe look is unusual but performance-wise a very average hybrid.” 4.5 male all court player using Head i.S2 strung at 56 pounds LO (Tournafiber Irradiated 16)

“I didn’t find this polyester hybrid to have any outstanding qualities. I only played 5 hours before it broke. I assumed the thickness of the mains would hold up a little longer. I found that it grabbed the ball pretty well, but all other aspects were average.” 5.0 male all court player using Prince Tour Diablo strung at 65 pounds CP (Wilson Sensation 17)

“Cut the string out after 30 hours and it still was not close to breaking. I developed some soreness in the arm. Certainly this will be an option for a big string breaker.” 5.0 male all court player using Head i.S6 strung at 58 pounds CP (Wilson NXT 17)

“I thought that the slightly textured main strings might make stringing the crosses a bit problematic, but the thin gauge crosses were no problem at all. Quite responsive for even a partial poly job (although I have never tried a nylon main/poly cross hybrid before), and really a surprising amount of feel. Nowhere near the stiffness of a typical all-polyester strung racquet.” 4.0 male all court player using Pro Kennex 7g strung at 57 pounds CP (Klip Excellerator 17)

“This string had very little power at first, but once it lost about four pounds in the first hour of play, the power improved. The best thing about this string is its durability. String breakers will love it. Everything else is only so-so.” 4.5 male all court player using Head Radical OS strung at 65 pounds LO (Gamma Advantage 15L)

“I didn’t find anything new with this string. it played average and didn’t have enough bite for my liking.” 5.0 male all court player using Babolat Pure Drive strung at 58 pounds CP (Tecnifibre E-Marix 17)

“An average string.” 4.0 male all court player using Fischer Pro Extreme FT strung at 65 pounds CP (Babolat VS Gut 17)

“Although there was no fraying, peeling, or buzzing, there was significant tension loss from the beginning, and things went down hill from there. The strings moved all over the place. The strings feel dead as a door nail. Why put polyester strings in the crosses? I couldn’t wait to cut them out.” 5.0 male all court player using Head i.S6 OS strung at 61 pounds LO (Wilson NXT 16)

“And yet another “poly string,” and as with most of the others, tension loss is very fast-10-14 lbs in just a couple of hours. Control and comfort are almost nonexistent. A useless string for a precision player or doubles specialist. Might be of some use for “slug um” baseliners, but that’s about all. I would not stock this string, nor would I recommend it for most club players.” 5.0 male all court player using Wilson Hyper Pro Staff Surge 5.1 strung at 58 pounds CP (Tecnifibre 515 Gold PS 17)

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

Playtester ratings

(compared to other strings)
No. of testers who said it was:
much easier 0
somewhat easier 9
about as easy 12
not quite as easy 11
not nearly as easy 2
(compared to the string played most often)
No. of testers who said it was:
much better 1
somewhat better 6
about as playable 10
not quite as playable 12
not nearly as playable 5
(compared to other strings of similar gauge)
No. of testers who said it was:
much better 10
somewhat better 13
about as durable 10
not quite as durable 1
not nearly as durable 0
RATING AVERAGES (From 1 to 5 (best)
Playability 3.2
Durability 4.1
Power 3.1
Control 3.5
Comfort 2.9
Touch/Feel 2.9
Spin Potential 3.3
Holding Tension 3.4
Resistance to Movement 4.0

See all articles by

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.



TI magazine search

TI magazine categories

TI magazine archives


Movable Type Development by PRO IT Service