Tecnifibre 4S is a square co-polyester tennis string designed to maximize spin and control for aggressive players. It was previously sold as Black Code 4S. The current name is shorter, but independent retailer information confirms that the underlying string is the same product.
Four pronounced sides provide direct ball bite, while Tecnifibre’s Thermocore process adds some flexibility to the firm monofilament. Independent playtesting found exceptional control, strong spin, low power and a surprisingly usable feel for such a demanding string.
4S targets advanced players and strong intermediates with long, fast swings. It is especially relevant to heavy-topspin baseliners who want a low launch and substantial physical resistance. The Tennis String Finder can help determine whether this specialized polyester fits your needs.
Tecnifibre 4S Rating
| Category | Rating |
|---|---|
| Power | 4/10 |
| Spin | 9/10 |
| Comfort | 5.5/10 |
| Control | 9/10 |
These ratings closely reflect independent playtesting, which identified spin and control as the clear strengths and power as the principal limitation.
Tecnifibre 4S Specifications
| Specification | Details |
|---|---|
| String type | Co-polyester monofilament |
| Composition | Flexible co-polyester compound |
| Manufacturing process | Thermocore heating and cooling process |
| Profile | Square, with four sides |
| Surface | Shaped and smooth, with no separately named coating in the official specification |
| Common gauges | 18 / 1.20mm, 17 / 1.25mm and 16 / 1.30mm |
| Common color | Black |
| Set and reel lengths | Approximately 12m sets and 200m reels |
| Made in | France |
4S is the renamed Black Code 4S. Gauge and package availability can vary by market.
Material and Construction
4S uses a single co-polyester filament. Tecnifibre blends polyester materials for control, resistance and enough flexibility to prevent the response from becoming entirely rigid.
Thermocore applies multiple heating and cooling stages during production. Tecnifibre uses the process to soften polyester’s natural stiffness while preserving a direct monofilament response.
The defining feature is the square cross-section. Four edges increase friction with the ball, helping advanced players produce spin when they supply fast vertical acceleration.
The official technical listing does not name a separate exterior coating. Performance should be attributed to the square geometry, smooth movement, low power and player-generated racket-head speed.
Tecnifibre 4S Performance
Power
4S is very low powered. Independent testing gave it one of the lowest power scores in the Tecnifibre performance range and found that it demands aggressive acceleration.
That restraint is useful for accomplished hitters. Players can take large cuts at the ball and create their own pace without receiving excessive rebound from the stringbed.
The string does not generate depth for compact swings. Beginners and defensive players may leave routine balls short unless their racket provides substantial power.
The 1.20mm gauge offers the most response, but even the thin version retains a control-first character.
Power rating: 4/10
Spin
Spin is 4S’s defining performance quality. The square profile presents four edges to the ball, and the controlled launch lets players accelerate upward aggressively.
Independent playtesting produced an excellent spin score. Testers found both direct grip and effective string movement, supporting topspin, slice and sharply dipping trajectories.
The 1.20mm and 1.25mm gauges provide the easiest interaction and snapback. The 1.30mm version is more stable and resistant in open patterns.
No shaped string creates spin without technique. 4S best rewards players who already produce racket-head speed and use a pronounced low-to-high swing path.
Spin rating: 9/10
Control
4S provides exceptional control for fast swingers. Its low power, firm construction and spin-assisted trajectory allow aggressive players to aim near the lines with confidence.
Independent testers consistently identified control as the main advantage. The string was particularly effective when paired with full swings that would make a livelier setup difficult to restrain.
The response is direct and comparatively low launching. This can support returns, attacking groundstrokes and precise serving, but it may feel unforgiving on incomplete contact.
Control can deteriorate after tension loss, notching or reduced snapback. Players should not wait for the durable string to break before reassessing it.
Control rating: 9/10
Comfort and Feel
4S is firm and demanding in the broader string market. Thermocore provides some category-relative flexibility, but the square monofilament remains less forgiving than nylon, multifilament or natural gut.
Independent testers produced mixed individual comfort scores. They generally found the string tolerable for experienced polyester users and noted useful pocketing, while still warning that it is unsuitable for beginners and sensitive arms.
The feel is direct, controlled and slightly dampened rather than plush. Lower-powered feedback can help accomplished players judge depth and touch once the setup is matched correctly.
Racket stiffness, gauge and reference tension strongly affect comfort. A reassuring review cannot guarantee the same physical response for every player.
Comfort rating: 5.5/10
Durability and Tension Maintenance
4S offers very strong resistance to breakage. Tecnifibre recommends it for heavy string breakers, and independent testing gave it high durability marks.
The square intersections can notch under repeated movement. Thinner gauges provide greater response but give the edges less material to resist wear.
Independent testing also found above-average laboratory tension maintenance and good playability duration for polyester. Individual testers still experienced response changes on different timelines.
Physical durability must be separated from useful playability. Replace 4S when the bed becomes erratic, harsh or unable to return efficiently, even if the monofilament remains intact.
Choosing the Right Gauge
4S is available in three standard performance gauges.
| Gauge | General characteristics |
|---|---|
| 18 / 1.20mm | Greatest bite, response and feel, with the least physical lifespan |
| 17 / 1.25mm | Balanced spin, control, feel and resistance |
| 16 / 1.30mm | Maximum stability and durability, with the lowest power and firmest bed |
The 17 / 1.25mm gauge is the best general starting point. Heavy breakers and very open patterns may benefit from 16 gauge.
Full Bed or Hybrid Setup
Full Bed
A full bed produces the clearest version of 4S’s low-powered spin and control. It is intended for experienced polyester users with long, fast strokes.
The setup can feel demanding in a stiff or low-powered frame. Gauge and reference tension should be chosen conservatively.
Tecnifibre 4S in the Mains With Softer Crosses
4S mains preserve the square string’s direct bite and control. Natural gut or multifilament crosses can add power, pocketing and comfort.
The four edges can cut into a soft cross, reducing the hybrid’s physical lifespan. A smooth and resistant cross is normally the more practical match.
Softer Mains With Tecnifibre 4S in the Crosses
Natural gut or multifilament mains emphasize comfort and power. 4S crosses add firmness and reduce launch.
The square profile may abrade the soft mains and restrict their sliding movement. A round polyester cross is usually preferable when preserving main-string snapback is the priority.
General Tension Guidance
4S should generally be installed below the reference used for nylon or multifilament. Its very low power and firm shape already provide substantial control.
Players moving from another firm polyester can start near their familiar range. A modest reduction may improve pocketing, but large changes can alter launch and string movement.
Gauge, frame stiffness, head size and pattern all affect the result. The thick gauge in a dense pattern will be especially demanding.
Use the Tennis String Tension Calculator for a broad starting point, then adjust in small steps within the racket manufacturer’s range.
Who Should Use Tecnifibre 4S?
4S is best suited to:
- Advanced players and strong intermediates
- Heavy-topspin baseliners
- Players with long, fast swings
- Frequent string breakers
- Users seeking very low power and high control
- Experienced polyester players who value direct feedback
Who Should Avoid Tecnifibre 4S?
4S is less suitable for:
- Beginners and developing juniors
- Players with compact or slow swings
- Users who need easy depth
- Players with arm sensitivity
- Anyone seeking plush feel
- Hybrid users who need a smooth, low-abrasion cross
Pros and Cons
| Pros | Cons |
|---|---|
| Exceptional spin potential | Very low free power |
| Outstanding control for fast swings | Firm, demanding response |
| Four-sided profile creates direct bite | Unforgiving on incomplete contact |
| Strong physical durability | Shaped edges can abrade soft hybrids |
| Above-average polyester tension performance | Requires developed racket-head speed |
| Three practical gauges | Comfort remains limited in the broader market |
Tecnifibre 4S Compared With Other Strings
4S vs Tecnifibre Black Code
Tecnifibre Black Code has five sides and a more moderate, muted response. 4S has four more pronounced edges, less power and a more specialized spin-and-control profile.
4S vs Prince Vortex Triad
Prince Vortex Triad uses a triangular construction for extreme bite. Both target aggressive spin, while 4S provides a firmer and lower-powered square response.
4S vs Solinco Hyper-G
Solinco Hyper-G is another four-sided control polyester. Both reward fast swings, but feel, gauge range and tension behavior can determine the better match.
4S vs Prince Tour XC
Prince Tour XC is round and prioritizes smooth snapback and controlled consistency. 4S adds direct geometric bite and a more aggressive spin focus.
Final Verdict
Tecnifibre 4S is a specialized spin-and-control string for accomplished players. Its square co-polyester construction, Thermocore process and low power create a direct platform for very fast swings.
Independent testing confirms its strengths while keeping the marketing in context. Spin, control, durability and playability duration are strong, but easy power and absolute comfort are not.
For advanced topspin players who generate their own pace, 4S is a compelling option. The 17 / 1.25mm gauge provides the best overall balance, while heavy breakers can move to 16 / 1.30mm.
Frequently Asked Questions
Is Tecnifibre 4S the same as Black Code 4S?
Yes. Independent retailer information confirms that the product was renamed from Black Code 4S to 4S.
What shape is Tecnifibre 4S?
It has a square cross-section with four edges designed to increase ball friction and spin.
Is Tecnifibre 4S powerful?
No. It is a very low-powered polyester intended for players who generate pace with fast swings.
Is 4S comfortable?
It has usable category-relative comfort for some experienced polyester users, but it remains firm compared with soft-string materials.