Tennis String Types Explained
Short answer: Most tennis strings are polyester (a firm, solid monofilament), synthetic gut (a nylon solid core with an outer wrap), multifilament (many fine fibres twisted together), or natural gut (cow intestine). A hybrid puts one in the mains and another in the crosses. In laboratory tests polyester loses the most tension and natural gut the least, so material is the first thing that moves your starting tension: Wilson’s published starting range is about 6 lbs (2.7 kg) lower for polyester than for nylon or gut.
The main tennis string types compared
Each row combines what the sources below support. The starting ranges are Wilson’s published first-string ranges in pounds, with kilograms converted here; they are where testing begins, not a rule for your racquet.
| Type | How it is built | Typical character | Tension loss (lab order) | Wilson starting range |
|---|---|---|---|---|
| Polyester (co-poly) | One solid extruded strand (monofilament) | Firm and durable; Wilson groups it with control and spin strings | Most | 44–54 lbs / 20.0–24.5 kg |
| Synthetic gut (nylon) | Solid nylon core with an outer wrap of thinner fibres | General-purpose nylon; Wilson groups nylon with power and comfort strings | Middle | 50–60 lbs / 22.7–27.2 kg (nylon/gut band) |
| Multifilament | Many small filaments twisted together, no solid core | Made to imitate natural gut; Wilson groups it with comfort strings | Middle (nylon) | 50–60 lbs / 22.7–27.2 kg (nylon/gut band) |
| Natural gut | Spun cow-gut fibres, polished and coated | Flexible, elastic, holds tension well; costly and sensitive to moisture | Least | 50–60 lbs / 22.7–27.2 kg (nylon/gut band) |
| Hybrid | One string in the mains, another in the crosses | Mixes two materials, often polyester with gut or nylon | Depends on the pair | 46–56 lbs / 20.9–25.4 kg, polyester about 2 lbs lower |
Wilson publishes one combined range for nylon and natural gut. String Tension AI applies that band to synthetic gut, multifilament and natural gut, the same way our tension chart by string type does. The lab order comes from one Tennis Warehouse University test series, so treat it as a direction, not a percentage you can expect in your racquet.
How each type of string is built
Natural gut
The first lawn tennis racquets were strung with sheep intestine. After the Second World War, makers moved to cow gut, which is still the source today. According to the International Tennis Federation (ITF), the fibres are cleaned, spun, dried, polished to the required diameter and finished with a polyurethane coating. The ITF describes gut as remarkably well suited to providing flexibility, elasticity and retention of tension, and gives its two drawbacks as cost and mediocre durability against wear and moisture.
Synthetic strings: nylon, polyester and kevlar
The ITF says synthetic strings are made mainly from nylon, polyester or kevlar, alone or combined, as either a single solid strand or up to hundreds of small filaments. The molten polymer is extruded and then stretched to strengthen it. Three constructions follow from that:
- Solid core with a wrap. A core strand protected by an outer wrap of thinner fibres, which the ITF says is usually added to protect the core and improve durability. Synthetic gut is the familiar example.
- Multifilament. The core is replaced entirely by small filaments twisted together, in the ITF’s words “in an attempt to recreate spun natural gut”.
- Monofilament. One solid strand. Wilson describes polyester as monofilament and nylon as multifilament in its string guide.
The ITF adds that no synthetic construction has natural gut’s low dynamic stiffness, or “feel”. Nylon is the most common man-made material, while polyester and kevlar are used to make strings more durable.
Polyester
Wilson’s string guide calls polyester stiffer and control-oriented and recommends it for advanced players, with natural gut and nylon suggested for beginners and intermediates because of their power and comfort. In Tennis Warehouse University testing, polyester also moved more across the stringbed than nylon or gut and produced more spin, though the authors stress that swing speed and swing angle matter more than the string.
To see which family a specific string belongs to, our tennis string database lists the material, construction, shape and gauges that each manufacturer publishes for its strings, with the source for every row.
How string material changes tension
Every string starts losing tension as soon as it is installed. In Tennis Warehouse University’s laboratory tests, strings lost up to 15 lbs (about 6.8 kg) within a minute of being strung on the test machine and more again on the first few impacts. Polyester lost more than nylon, which lost more than natural gut.
Losing more tension does not make a string feel softer. The same tests found that a stiffer polyester can still give a stiffer stringbed than a softer nylon that has lost only a few pounds. That is why makers start polyester lower: Wilson’s range for polyester is 44–54 lbs (20.0–24.5 kg) against 50–60 lbs (22.7–27.2 kg) for nylon and gut, and Luxilon says its polyester strings perform well at lower tensions.
Two practical consequences follow:
- Change one thing at a time. If you switch material and tension together, you cannot tell which change you are feeling. Our string tension calculator starts from your frame’s printed range and the construction you choose.
- Compare readings with the same setup’s baseline. A fresh polyester bed and a fresh gut bed drift at different rates, so take a baseline after each string job and track how stringbed tension changes over time against that baseline, not against another string.
Hybrid strings
A hybrid uses one string in the mains (the long strings) and another in the crosses. Babolat says the blend of natural gut and polyester is still the most common hybrid, and that hybrids let a stringer adjust gauges, tensions and the choice of mains and crosses separately. Wilson gives polyester mains with nylon crosses as an example that mixes control and spin with power and comfort.
For tension, Wilson suggests stringing the polyester part about 2 lbs (1 kg) lower than the nylon part. Which string goes in the mains changes the result more than most players expect; the hybrid mains, crosses and split-tension guide covers orientation and split tensions in detail.
Choosing a string type
These rules are String Tension AI’s reading of the sources above. They are starting points to test, not a ranking.
- You want comfort and easy depth: start with a multifilament, synthetic gut or natural gut, the materials Wilson groups as power and comfort strings. The guide to string tension and arm comfort sets out what the evidence says about softer materials and impact shock.
- You break strings often or want a firmer, control-oriented feel: try polyester, starting toward the lower part of your frame’s range.
- You want polyester’s durability with a softer feel: try a hybrid with polyester in one direction and gut or nylon in the other.
- You are new to a material: keep your racquet, gauge and tension the same for one string job, so the change you feel is the material.
Once you have a material, the next choices are thickness and pattern. The tennis string gauge guide explains how thinner and thicker strings differ, and string pattern and tension explains why the same reference tension feels different in an open or dense pattern. Unfamiliar terms are defined in the tennis stringing glossary.
Tennis string types: FAQ
What is the difference between polyester and synthetic gut?
Polyester is usually a single solid strand and is firmer and more durable; synthetic gut is a nylon core with an outer wrap and is a softer general-purpose string. In laboratory tests polyester also lost more tension than nylon, so makers suggest stringing it lower: Wilson’s starting range is 44–54 lbs for polyester and 50–60 lbs for nylon and gut.
Is multifilament the same as natural gut?
No. A multifilament is a synthetic string made from many small filaments twisted together, designed to imitate spun natural gut. Natural gut is made from cow intestine. The ITF notes that no synthetic construction matches natural gut’s low dynamic stiffness, while gut costs more and is less resistant to wear and moisture.
Which string type holds tension best?
In Tennis Warehouse University laboratory tests, natural gut lost the least tension, nylon more, and polyester the most. Losing more tension does not mean a softer stringbed, though: a stiff polyester can still feel firmer than a nylon that has lost only a few pounds. Measure your own racquet fresh and compare later readings with that baseline.
Should I change tension when I change string type?
Usually yes, because material sets the starting range. Wilson starts polyester about 6 lbs lower than nylon or gut, and about 2 lbs lower than nylon within a hybrid. Keep the new tension inside the range printed on your racquet, change one thing per string job, and take a fresh baseline reading so you can compare like with like.
What the sources support
The ITF document supports how each material is made and its general properties. Tennis Warehouse University’s laboratory tests support the order of tension loss and string movement by material. The starting ranges, player-level suggestions and hybrid advice are manufacturer guidance. The comparison table and decision rules are String Tension AI’s synthesis.
Accessed October 3, 2026
- International Tennis Federation — Rackets and Strings: Strings (November 2019) for natural gut, synthetic materials and constructions, and gut’s low dynamic stiffness (governing-body technical guidance).
- Tennis Warehouse University — How Tennis Strings “Go Dead”, Part 1 for tension loss after stringing and the order of loss by material (laboratory testing).
- Tennis Warehouse University — String Snap-Back and Spin for polyester moving more and producing more spin than nylon or gut, and the larger role of swing speed and angle (laboratory testing).
- Wilson — How to Choose Tennis String (updated January 18, 2024) for string categories, monofilament and multifilament, and hybrid examples (manufacturer guidance).
- Wilson — What String Tension Should I Use in My Tennis Racket? for starting ranges by material and the 2 lb (1 kg) polyester offset in hybrids (manufacturer guidance).
- Babolat — Tennis Hybrid for gut and polyester as the most common hybrid and adjusting mains and crosses separately (manufacturer guidance).
- Luxilon — Common Stringing Mistakes to Avoid for the note that its polyester strings perform well at lower tensions (manufacturer guidance).
See how your string type holds tension
Measure the racquet fresh after stringing, then compare later readings with that baseline to see how your material settles in your racquet.
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