Tennis String Types: Polyester vs. Multifilament vs. Natural Gut (and Gauge)
Quick answer: There are four main types of tennis string. Polyester is stiff and durable and gives control and spin. Multifilament is soft and arm-friendly with good power. Synthetic gut is an affordable all-rounder. Natural gut is the softest, liveliest string with the best tension holding. Thinner gauges add feel and spin; thicker gauges last longer.
String choice changes how a racquet plays as much as the frame does. This guide covers what strings are made of and how thick they are. To choose a tension, see our tennis strings buying guide, and to combine two strings in one racquet, see our hybrid stringing guide.
What are the main types of tennis strings?
| Polyester (co-poly) | Multifilament | Synthetic gut | Natural gut | |
|---|---|---|---|---|
| Construction | Single solid polyester filament, often blended (co-poly) | Hundreds of thin nylon or similar fibers bundled and bonded | Solid nylon core with one or more outer wraps | Twisted cow intestine (serosa), coated |
| Feel | Stiff, firm | Soft, comfortable | Medium | Softest, most elastic |
| Power | Low | Medium to high | Medium | High |
| Spin and control | Highest spin potential; most control | Moderate | Moderate | Good, with excellent feel |
| Durability | High (resists breaking) | Lower; fibers fray | Medium | Low to medium; sensitive to moisture |
| Tension holding | Poor; loses tension and goes “dead” | Very good | Average | Best |
| Arm comfort | Least arm-friendly | Very arm-friendly | Fairly arm-friendly | Most arm-friendly |
| Best for | Frequent string breakers, big hitters, spin players | Players wanting comfort and power, arm issues | Beginners, budget-minded players | Players who want the best feel and comfort |
How stiff is each type of tennis string?
Stiffness is one of the clearest differences between string types. Tennis Warehouse University (TWU) measures the stiffness of hundreds of strings under the same conditions. Lower numbers are softer and more comfortable; higher numbers are firmer, with more control:
| String type | Strings tested | Median stiffness (lb/in) | Example strings (lb/in) |
|---|---|---|---|
| Natural gut | 18 | 94 | Wilson Natural Gut 16: 97; Babolat Tonic+ 16: 99 |
| Nylon (multifilament and synthetic gut) | 230 | 158 | Babolat Xcel 16: 151; Wilson NXT 16: 174; Prince Synthetic Gut 16 Duraflex: 178 |
| Polyester | 483 | 201 | Luxilon ALU Power 16L: 209; Babolat RPM Blast 16: 233 |
Source: TWU String Stiffness Tool (strings measured at a 52 lb reference tension in a simulated 120 mph serve impact). Values vary by model and gauge.
What are polyester strings?
Polyester (or co-poly) strings are made from a single solid filament. They’re the stiffest type, which gives a low-powered, controlled response, and their slick surface lets the main strings slide and snap back for extra spin. They’re also the most durable, so many players who break strings often use them. The trade-offs are harshness and tension loss. Poly loses tension faster than nylon or gut, and once it goes “dead” it feels stiff and loses its snapback. Players who use poly should restring more often than players using softer strings; see how often to restring your racquet. Some brands recommend poly mainly for older juniors and adult competitive players.
What are multifilament strings?
Multifilament strings bundle hundreds of thin fibers, usually nylon, into a single string. That construction makes them soft, elastic and arm-friendly, with good power and a feel that’s closer to natural gut than any other synthetic. They’re a popular choice for players with arm discomfort and for players who want easy power. Their main downside is durability: the fibers fray and eventually break, especially for big spin hitters.
What is synthetic gut?
Synthetic gut is a solid nylon core with outer wraps. It’s the classic all-round string: medium feel, power and durability at an affordable price. It’s a good starting point for beginners and recreational players, and many pre-strung racquets come with a nylon string. If it feels harsh or breaks often, move to a multifilament for comfort or a polyester for durability.
What is natural gut?
Natural gut is made from twisted strands of cow intestine and is the original tennis string. It’s the softest, most elastic and most powerful string, and it has the best tension maintenance of any string type. It’s also the most expensive, and it’s sensitive to moisture. Many players pair natural gut with a polyester in a hybrid to combine its feel with the durability and control of poly; see our hybrid stringing guide.
What does tennis string gauge mean?
Gauge is the thickness of the string. Higher gauge numbers are thinner. An “L” (for “light”) after the number, such as 16L, means roughly halfway between two gauges. There’s no universal gauge standard, and one brand’s 16 can be another’s 16L, so the millimeter size printed on the package is the best guide. In general, thinner strings give more power and spin, and thicker strings give more control and durability.
| Gauge | Diameter (mm) | Typical character |
|---|---|---|
| 15 | 1.35–1.40 | Thickest; most durable; most control |
| 16 | 1.25–1.30 | Balanced durability and feel; very common |
| 17 | 1.20–1.25 | More feel, power and spin; less durable; very common |
| 18 | 1.15–1.20 | Thin; strong feel and spin; breaks sooner |
| 19 | 1.10–1.15 | Thinnest; maximum feel; least durable |
Rough millimeter ranges from Tennis Warehouse. There is no universal gauge standard, so compare the millimeter size on the package.
Should I use 16 or 17 gauge strings?
Choose 16 gauge if you break strings often or want them to last longer. Choose 17 gauge if you want more feel, a little more power and more bite on the ball for spin, and you don’t mind replacing strings more often. If you break a 17 quickly, move up to a 16; if a 16 feels dull, try a 17.
Which tennis string type should I choose?
- You’re a beginner or play casually: start with synthetic gut, or a multifilament for more comfort.
- You have arm or elbow discomfort: try multifilament or natural gut, and avoid full polyester.
- You break strings often or hit with heavy spin: polyester, or a poly hybrid.
- You want the best feel and don’t mind the cost: natural gut, or a gut and poly hybrid.
Browse our tennis strings, or ask about a string consultation at our racquet services page.
The bottom line
Polyester gives control, spin and durability. Multifilament gives comfort and power. Synthetic gut is the affordable all-rounder, and natural gut is the softest and liveliest. Use gauge to fine-tune durability and feel, then pick a tension with our tennis strings buying guide.
Frequently asked questions
What is the most arm-friendly tennis string?
Natural gut is the softest and most elastic string, followed by multifilament. In TWU stiffness testing, natural gut had a median stiffness of 94 lb/in, compared with 158 for nylon strings and 201 for polyester.
Do polyester strings give more spin?
Polyester has the highest spin potential. Its slick, stiff strings slide and snap back during impact, which adds spin. Technique matters more than string type, though.
What is a co-poly string?
Co-poly is a polyester string blended with other materials, which makes it softer or more elastic than pure polyester. Today almost all polyester strings are co-polys.
Is thinner tennis string better?
Not always. Thinner strings give more feel and spin and a little more power, but they break sooner. Thicker strings last longer. The best gauge balances feel with how quickly you break strings.
Can I mix two types of string in one racquet?
Yes. That’s called a hybrid. A common setup uses polyester in the mains for durability and spin and a multifilament or natural gut in the crosses for comfort. See our hybrid stringing guide.