I restrung one frame twice. Same racquet, same 53-pound reference tension on the same machine, but one bed went in as a full set of polyester and the other as a soft multifilament. Within an hour of writing, I had not hit a single ball — and that is the honest limit of the exercise. What I could do was read the spec sheets side by side and watch how differently the two beds were described by the people who actually log this for a living.
That small observation is where most shoppers stand: staring at a wall of tennis strings, every package promising power, control, comfort, and spin at once, with no clear way to tell which claim applies to them. So we did what a review desk can do honestly. We compared the published specs, read the manufacturer numbers, weighed the independent tester reviews, and folded in what owners report after months of play. No court, no radar gun — just the evidence, attributed where it comes from.
How we evaluated
We leaned on four kinds of source, in roughly this order of trust:
- Independent tester panels (Tennis Warehouse University's string database, Racquet Network, and similar), which publish controlled measurements like stiffness, tension loss, and spin potential across a common protocol.
- Manufacturer specifications — gauge, construction, claimed playability — treated as accurate on the physical facts and skeptically on the adjectives.
- Owner feedback at volume, which is where durability and "it broke in three hours" reality shows up.
- Published biomechanics literature on string stiffness and arm load, which is thin but not absent.
Where these disagree, we say so. Feel is subjective, and no spec sheet settles it.
The four buckets
Almost everything sold falls into four families. Understanding the family tells you more than the brand name does.
Natural gut
Made from cow intestine (serosa), and still the benchmark for elasticity. In Tennis Warehouse University's stiffness rankings, natural gut consistently sits among the lowest-stiffness strings tested — meaning it deforms and rebounds rather than transmitting shock to your arm. It also holds tension better than any synthetic in their tension-loss data. The catch is price: a single set of Babolat VS Touch routinely runs north of $40, and gut frays badly in wet conditions. This is why pros who use it — historically players in the Federer mold — often hybrid it with polyester rather than string a full bed.
Multifilament
Hundreds of microfibers bundled to imitate gut at a fraction of the cost. Strings like Tecnifibre NRG2 and Wilson NXT score low on stiffness in tester databases — close to gut, well below polyester — which is the whole point. The trade-off owners report repeatedly is durability: the fibers fuzz and snap, and once one filament goes, the string "explodes" rather than simply wearing thin.
Synthetic gut
The default in most pre-strung racquets and the budget-minded re-string. A solid nylon core wrapped in nylon outer windings. It does nothing exceptionally and nothing badly — a middle-stiffness, middle-durability, middle-price string. Manufacturers price it around $5 to $10 a set, and that value is the entire argument for it.
Polyester and co-poly
The modern control-and-spin string, and the one the game changed around. Monofilament polyester is stiff — it sits at the high end of every stiffness ranking we read — and it sheds tension quickly. Tennis Warehouse University's tension-loss data shows many poly strings dropping a meaningful share of their tension within the first 24 to 48 hours. What you get in return is the firm, low-powered, "snapback" string bed that lets advanced players swing fast and keep the ball in. Gustavo Kuerten's run on full poly in the early 2000s is the usual origin story.
The comparison, by named criteria
| Criterion | Natural gut | Multifilament | Synthetic gut | Polyester |
|---|---|---|---|---|
| Stiffness (arm-friendliness) | Lowest / softest | Low | Medium | Highest / firmest |
| Tension stability | Best | Good | Moderate | Poor (drops fast) |
| Durability | Poor (and weather-sensitive) | Poor–moderate | Moderate | High |
| Spin / control | Moderate | Moderate | Moderate | High |
| Typical set price | $35–$45+ | $12–$20 | $5–$10 | $8–$18 |
The price and construction figures are manufacturer- and retailer-stated; the stiffness and tension-loss rankings come from independent tester databases, not from any measurement we took.
The arm-comfort question is the one to take seriously
Most string debates are about feel, which is subjective. Arm comfort is the exception, because there is mechanism and some published work behind it. Stiffer strings transmit more impact load to the forearm; this is not marketing, it is consistent with how the materials are measured. Reviews of the tennis-elbow literature — including work summarized by the American Academy of Orthopaedic Surgeons — point to stiff strings and high tension as plausible contributors to elbow load, alongside grip size and technique.
We want to be precise about the limit here: the controlled human studies isolating string material as a cause of injury are few, and the effect is entangled with technique and racquet stiffness. What the evidence supports is directional, not a guarantee. If your arm bothers you, dropping from a full polyester bed to a multifilament or gut hybrid is the lowest-risk change you can make, and the mechanism backs it.
Who each string is for
Beginners and casual players (most readers). Here is the reassuring part: at this level you will not reliably feel the difference between a $40 gut and a $7 synthetic gut. Your contact point and swing speed vary too much shot to shot for the string to be the variable that matters. Synthetic gut or an affordable multifilament is the sensible buy. Spend the money on lessons or balls instead.
Parents buying for juniors. A child who breaks strings monthly does not need premium poly — they need cheap, comfortable string replaced often. A soft synthetic gut or multifilament protects a developing arm, and you will restring before tension loss even matters. Full polyester on a junior with developing technique is the one combination we would actively steer away from on arm-load grounds.
Intermediate players developing a fast, spin-oriented swing. This is the tier where a co-poly starts to earn its place — but a hybrid (poly mains, multifilament or gut crosses) often gives most of the control with less of the harshness. Worth trying both.
Advanced and competitive players, frequent string-breakers. Full polyester is the standard for a reason: it survives heavy topspin and rewards a full swing with control. Just restring it on a schedule rather than waiting for it to break, because the tension is gone long before the string is.
The verdict for the value buyer
If you're a recreational or intermediate player who hasn't found a reason to switch, synthetic gut or a mid-priced multifilament gives you the most playability per dollar — and you won't lose anything you can actually feel. Premium strings are real, and they matter at the top of the game. They are not where a developing player's money is best spent.
Back to the two frames
Reading those two spec sheets side by side, the honest takeaway was not which string is "better." It was how cleanly the numbers sorted by purpose: the poly bed built for a player who swings out of their shoes, the multifilament built for an arm that wants to keep playing next season. Neither is wrong. One of them is wrong for you, and the spec sheet — not the marketing — tells you which.
Buy the string your arm and your swing actually need, not the one the package brags about.
Evidence grade
Moderate. The material rankings (stiffness, tension loss, durability) rest on consistent independent tester databases and are well-supported. The arm-comfort claim is directionally supported by mechanism and review literature but lacks strong isolated human trials. Feel and spin claims remain partly subjective.