Comments: Reading reviewers' comments here saying this is closest string to natural gut, or just like gut, I am scratching my head. To me, this string is nothing remotely like natural gut. Read for yourself Tennis Warehouse product description which says good dampening and a slightly muted feel, and less lively string than NXT or NRG2. Now that doesn't sound like the characteristics of natural gut to me, but all things are relative. To me, this string is much closer to a soft poly than natural gut. The stiffness is on par with a soft poly. Note that the gauge is really 18 gauge or 17L gauge as the diameter is 1.20mm. That helps its playability. The one thing I do like about this string is minimal string movement. I started with higher tension as recommended, but found that too boardy and ended up lowering tension twice to below my normal tension. If you are looking for soft polyesters, there are better and cheaper alternatives, many of them have similar tension retention. If you are looking for gut-like multifilaments, definitely look elsewhere.
From: Basil, 6/28/20

Comments: In the last year, I suffered a lot from Tennis Elbow and Golfers Elbow. I tried many raqcquets and many strings, but every time I played I had to take a break of few months before I could try again. The pain was too much, after about an hour of play. Yesterday, I tried this string, on Prince O3 MP, my old favorite -- thankfully didn't sell it! And it was O.K.! Not only I fely my movement was good, hitting the ball precisely, the impact was also very accurate and most importantly - I almost didn't feel any pain! Well, recently I tried KLIP 15 / HEAD Velocity 16, in Volkl V-SENSE 10 325 and it was awful! So, really, don't believe all the bad reviews, at least, it's a very good string for me!
From:Reuven, 6/23/19

Comments: Highly recommend these strings! They provide the kind of feel, control, and durability that a quality multifilament string should provide. Recommendations for higher tension and waxing mains are spot on. They're the closest string to natural gut I've found.
From:Ray, 10/2/17

Comments: Follow up to my post from 7 years ago below. I have stayed with Iso-Speed Professional Classic 17 and still play with two Pure Drive + racquets. The magic stringing formula for me is: Mains at 68 lbs and wax them well with Bohning Tex-tite bow string wax. Then, crosses at 66 lbs. (When using nylon strings, I used to string the same racquet at 54/52 lbs for comparable control, no wax.) This remains a great string for feel and power. Wax makes all the difference in durability. I re-string after 8 to 10 hours of play, at which point strings are frayed and shifting and too lively, but I have never broken a string when waxing the mains. Elbow issues never returned.
From:Paul, 12/13

Comments: I really like hitting with this string. Good power, control and feel. Used Natural Gut Mains 18 at 55 and Isospeed Pro 17 at 58. Very easy to string and no coil problems.
From:Fred, Columbus, OH, USA, 02/11

Comments: Trying it as a cross for a hybrid with MSV Hex, since it was the closest thing to the crosses of my previous favorite, Intellitour 17. Seems great, so I'm waiting with my fingers crossed to see its durability.
From:Noel, London, UK, 10/10

Comments: I've been trying to get the right setup for my Pure Drive cortex. After many strings I decided to try this out based on some good reviews. Boy, now it feels nice (just like gut) but lasts longer. Great feel, power, comfort. This string complements the stiffness of the PD well, try it out!
From:Eric, HI, USA. 8/08

Comments: I have been using this string in the mains with Head PPS 18 in the crosses. It is the best string that I have found. I get the most spin, it is softer than a polyester hybrid, and the tension lasts twice as long as a polyester hybrid. It is also less expensive than the polyesters that my arm will tolerate.
From:John, Surprise, AZ, USA. 12/07

Comments: After searching for a softer string to alleviate elbow pain (from Lux BB alu), I tried several Isospeed strings. I'm a 4.0 baseliner and hard hitter, using Babolat Pure Drive Team +. Here are my findings: Isospeed Control 16 (M's 59 lbs/X's 57 lbs): PROS: zero shifting of strings and no apparent tension loss after 2 hours. Very soft. CONS: Far too much action (need to retest at +5 lbs) Average bite. . .Isospeed Energetic 16 (M's 62 lbs/X's 60 lbs): PROS: durable, no tension loss. CONS: extreme string shift, too much action and no bite made it very difficult to generate spin. . .ISOSPEED PROF. 17 (M's 61 lbs/X's 60 lbs): PROS: soft, excellent feel, strong bite easily generated lots of spin, string bed generated ample power in direct and controlled proportion to swing speed. CONS: shifting of strings, fraying in sweet spot after two hours--durability questionable. (Elbow pain has subsided.)
From:Paul, Sherman, CT, USA. 3/07

Comments: I've been using Isospeed pro for several years and have never found a better string. Has a very comfortable, soft feel and gives excellent control. Not a very durable string but you always get warned before it breaks because it frays in a similar way to natural gut. A few months ago I switched to the Isospeed hybrid string and have found it to be every bit as good.
From:Lew, Brisbane, Australia. 12/06

Comments: Great, great string. First off, I have to say that one of my major pet peeves is excessive string movement. Even with my 18x20 M-Fils, my strings are usually all over the place after a few hard hits. Not with IsoSpeed Pro. Strings stay locked in place, giving me a consistent response from the stringbed. Control is excellent, power is tamed, and feel is good. It also makes the best hybrid cross ever. I string gut mains with Iso crosses at max tension and it plays amazingly well. I also hybrid Gosen for my practice and backup racquets and it works great. I'll never stop using this stuff!
From:Anonymous. 12/06

Comments: I've used this string in various player's racquets (off and on- alternating with gut or hybrids) for the last 6+ years and its still fairly difficult to categorize, but I seem to keep going back to it. It just has a unique feel and response off the stringbed. One feature I particularly like is how much tension you can use (I've gone up to 86 lbs. in some of the heavy, more flexible frames - Muster specs) yet still retains a good degree of power and comfort, as long as you don't hit late! Strung at the higher ranges the spin potential is nothing short of amazing. It certainly loses some tension immediately after stringing (about 6-8 lbs. in my experience), but sets in nicely there after. Plays exceptionally well at those higher tensions, but only for a few hours, then starts to lose its pop. If you like to string racquets on the way tighter side and have multiple frames to switch to after a few hours of play, I don't think you can find a better string, at any cost.
From:Barry, Los Angeles, CA, USA. 12/05

Comments: Not easy to string. The coating made it very tough to put in the crosses. I did as the package said and strung it 6 pounds tighter that I usually do, I did notice the tension did go down after 24 hours I just don't know how much. The strings did stay in place when I was hitting with it which was nice, given that the Bow Brand gut I was using is frayed from playing (5 Times). I would not say it hits like gut (has similar character), I would compare it to Tecnifibre NRG2. I can not comment on Durability as I have only hit with it a couple of times, but it seems like a good buy.
From: Jim, Boston, MA, USA. 03/05

Comments: I was not very impressed with the Iso-Speed Professional 17. I had a lot of pop when hit flat and in the sweetspot, but other strings could suffice and prove more economical such as Wilson Sensation.
From: Brian, Houston, TX, USA. 8/03

Comments: Looks and plays very similar to natural gut. After reading previous feedback thought I'd give it a try and although very pleased with performance the durability was really poor - broke after 6 hours. Iso-Speed give it 7/10 for durability and 10/10 for playability - agree with the playability score but be warned, if the manufacturer says 7/10 it probably means 3/10. If you're a serious player you're better off with Energetic 16, which lasts over twice as long - if you don't hit the ball that hard its a great string. Demoed the string in Volkl Cat 10 at 64lbs
From: Anthony, UK. 5/03

Comments: The Iso-Speed Professional 17 is a great kind of strings. The playability is awesome and the durability is great too! You have got to get it. It will improve your game.
From: Matthew, Endicott, NY. USA 4/02

Comments: Well, it's not the best reason to change strings but.... My stringer was out of Tecnifibre 17 NRG, so he talked me in to trying the Iso-Speed Pro 17. So far, I love it! It's softer feeling than the Tecnifibre and I feel like I can generate more spin. (3.5 level player using a Prince Warrior Midplus, strung at 58lbs). It also seems to be more durable.
From: Joel, TW Message Board post, USA 4/02

Comments:When strung properly, Iso-Speed Professional 17 doesn't lose tension as much as most other strings, however, its high elasticity together with the fact that its elasticity stays constant at all tensions gives a deceptive impression of tension loss. i.e. most strings have lost all their elasticity by the time the tension loss is noticeable, therefore giving a "dead" feel rather than a loose feel. With Iso-Speed, the tension loss is much more noticeable because of its high elasticity and you rarely get to the "dead" feeling stage.
From: Guru, TW Message Board post, USA 11/01

Comments: I got some Iso-Speed Professional 17 from TW and strung it up. It plays really well. It has a good bit of bite and feel as well. I really thought it played well - firm but not too firm. I have only hit with it for an hour or so, so we'll see how it does long term. Just for reference, I've been playing with Tecnifibre TR Pro SPL 17, which is on the softer side of the scale. The Iso-Speed Professional 17 played a little firmer, but not so much that it was uncomfortable.
From: Rabbit, TW Message Board post, USA 11/01

Comments: If you are looking for a better playing string than straight polyester, but want the durability of polyester, then this is the string for you. It has excellent feel and strings up nice.
From: Chris, Tacoma, WA. USA 11/01