String Tension and String Type: The Actual Differences

The racquet is the chassis. The strings are the engine of stroke performance. Two identical racquets strung differently play like different racquets. The numbers and material types printed on a string job — 24 kg tension, polyester, multifilament, hybrid — correspond to specific differences in how the racquet hits the ball and how the ball comes off the strings.

Most amateur players never adjust their strings. They use whatever the shop strung when they bought the racquet, and they replace strings only when they break. They are leaving performance on the table — sometimes a lot of it — because the wrong string at the wrong tension can suppress pace, restrict spin, increase arm load, or fail to deliver control. This article is a working introduction to what strings actually do and how to choose them.

What Strings Do

When a tennis ball strikes a strung racquet, three things happen at the moment of contact:

1. The strings deform. They stretch and move slightly, absorbing the ball’s impact energy. The amount of deformation depends on string material, gauge (thickness), and tension.

2. They release that energy. As the strings return to shape, they propel the ball back outward. The efficiency of this energy return — how much of the incoming kinetic energy comes back as ball speed — depends on string properties.

3. They impart spin. Strings that slide and snap back into position grab the ball and add topspin or slice. Strings that stay in position generate less spin. String material and design strongly affect this.

Different strings do all three of these things differently. Choosing a string is choosing a balance of power return, control, spin generation, comfort on the arm, and durability.

The Four Main String Categories

Most modern tennis strings fall into four categories.

Category 1: Polyester (often called “poly”). Stiffer, less elastic. Lower power return, higher control. Generates significant topspin because the strings slide and snap back, gripping the ball. Tougher on the arm because they transmit more shock. Lose tension faster than other categories. Used by the majority of competitive players.

Category 2: Multifilament. Many fine filaments bundled together to create a soft, elastic string. Higher power return, softer feel, gentler on the arm. Less spin generation than polyester. Less durable — breaks faster. Used by players prioritizing comfort and feel over maximum spin.

Category 3: Natural Gut. Made from animal intestine. Premium-priced, premium-performing. Highest power return, best feel, lowest arm load. Generates less spin than polyester but more than synthetic gut. Sensitive to humidity. Used by players who want the best feel and have the budget. Often used in hybrid setups (gut mains + poly crosses).

Category 4: Synthetic Gut. A mid-range monofilament, usually nylon-based. Decent power, decent control, decent durability, moderate price. Used by recreational and intermediate players as a default choice.

Most competitive players today use polyester or polyester hybrids (poly mains with synthetic gut or natural gut crosses). The hybrid approach combines the spin and control of polyester in the main strings with the feel and softness of another material in the crosses — a popular compromise.

What Tension Does

String tension — measured in kilograms or pounds — affects how the strings behave:

Lower tension (around 18-22 kg / 40-48 lbs): Strings deform more on contact. They release more stored energy as ball speed — the “trampoline effect.” Result: more power, softer feel, less control on aggressive swings. Often more comfortable on the arm.

Higher tension (around 24-28 kg / 52-62 lbs): Strings deform less. They release energy more abruptly. Result: more control, more precision on direction and depth, less power. Often harsher on the arm.

The relationship is roughly inverse: power and control trade off through tension. A player who wants more power lowers the tension. A player who wants more control raises it. The sweet spot for a given player depends on their stroke style.

What Players Should Actually Adjust

Five practical levers a player can move on their string job:

Lever 1: String material. Switch from synthetic gut to polyester for more spin and control. Switch from polyester to multifilament for more comfort. Add natural gut in a hybrid for premium feel.

Lever 2: String tension. Drop by 2-3 kg from the recommended center for more power. Raise by 2-3 kg for more control. Each 1 kg of tension change has noticeable feel differences for the player.

Lever 3: Gauge (thickness). Thinner strings (1.20-1.25 mm) generate more spin and have more feel but break faster. Thicker strings (1.30-1.35 mm) last longer but produce slightly less spin.

Lever 4: Hybrid construction. Mains and crosses can use different strings. Common combinations: poly mains for spin, multifilament or gut crosses for feel; multifilament mains for power, poly crosses for spin.

Lever 5: Restring frequency. Polyester loses tension within hours of stringing and continues degrading over weeks. Restringing more frequently than once strings break (every 10-15 hours of play for competitive players) maintains consistent feel and performance.

How to Diagnose String Issues

Players who suspect their strings are wrong should check for these symptoms:

Symptom 1: Frequent control errors despite normal mechanics. Balls flying long, balls going wide, balls in the net. This often indicates strings that are too low-tension or too elastic. Raise tension or switch to a less elastic material.

Symptom 2: Lack of pace despite full swing. Balls feel “dead” coming off the strings. This often indicates polyester strings that have lost tension or material that’s too dampening. Restring sooner or switch to more elastic material.

Symptom 3: Insufficient spin on aggressive shots. Balls landing flat without bite. Switch to polyester or hybrid setup, or to thinner gauge for more bite.

Symptom 4: Arm discomfort. Elbow soreness, forearm fatigue after sessions. Polyester is the most common culprit — too stiff, too low elasticity. Drop to multifilament or hybrid, lower the tension.

Symptom 5: Strings break unusually fast. Could indicate too-thin gauge, too-soft string, or technique putting unusual load on the strings (mishits, off-center contact). Adjust string thickness or address technique.

What Tour-Level Setups Look Like

A common ATP-level string job, illustrative not normative:

• Polyester mains (e.g., Luxilon Alu Power, Babolat RPM Blast)
• Polyester or natural gut crosses
• Tension: 22-25 kg (a typical range; varies widely)
• Restrung every 5-10 hours of play

Williams sisters and a few others use natural gut mains with poly crosses for premium feel. Federer used hybrid setups (poly mains, gut crosses) throughout his career. Modern young players overwhelmingly use polyester.

This is not a recipe to follow — amateur players don’t need pro-level tension or pro-level restring frequency. The takeaway is that even at the top level, string choice is highly individualized. There is no one right setup.

Pricing and Restring Strategy

A realistic budget framework for amateur players:

Recreational/club player (1-2 sessions/week): Mid-range synthetic gut or multifilament, restring when strings break (typically every 2-4 months). Total cost: $80-200 per year in string and labor.

Competitive amateur (3-5 sessions/week): Polyester or hybrid setup, restring every 6-10 weeks regardless of breakage. Total cost: $200-400 per year.

Serious competitive amateur (5+ sessions/week, tournament play): Polyester or hybrid, restring every 3-4 weeks. Total cost: $400-700 per year. Consider learning to string your own to save labor costs (a one-time investment in a stringing machine pays back over years).

These numbers are approximate but realistic for major tennis markets. The investment in strings is one of the lowest-leverage equipment expenses; spending more on strings produces more measurable performance benefit than spending more on the racquet itself.

A Few String Myths to Dispel

Myth 1: “Higher tension equals more power.” False. The relationship is the opposite — lower tension typically produces more power, because the strings deform more and release more energy.

Myth 2: “Polyester ruins your arm.” Polyester is harsher on the arm than gut or multifilament, but it doesn’t automatically cause injury. Many players use poly for years without issues. The risk is real but manageable through tension reduction, hybrid setups, or careful gauge selection.

Myth 3: “Strings are the same once you string them in.” Polyester strings lose 10-20% of tension within the first 24 hours of stringing, and continue losing tension over weeks. The “stringbed” you played with at hour 5 is not the same as at hour 20. This is why competitive players restring before strings break.

Myth 4: “Restringing is too expensive.” A polyester restring costs roughly $20-50 depending on the shop and the string. The performance difference between fresh strings and old strings can be substantial. The cost-per-improvement is competitive with any other tennis-related expenditure.

One Thing to Do on Court Tomorrow

If you’ve been playing with the same strings for more than four months, get a restring. Use the same string and tension you currently have, just fresh. Play a session with the new strings. Most players, doing this for the first time, are surprised at how much more control and feel a fresh stringbed offers.

If you’ve never experimented with strings, ask your shop to recommend one alternative — a poly if you’ve been on synthetic gut, a multifilament if you’ve been on poly. Try it for a few sessions. Notice the differences in spin, control, and arm comfort.

The strings are the engine. Most amateur players have an engine they have never tuned. Tuning it is among the highest-leverage equipment changes available to a tennis player — it costs little, requires no technique change, and produces immediate measurable difference.

About the author: Emre Köse is a tennis coach at Beykoz Tenis Kulübü in Istanbul, with 12+ years on court. He holds a BSc in Coaching Education from Marmara University, Faculty of Sport Sciences.

Related in this series: Racquet specs explained · Tennis shoes: surface-specific design · Tennis elbow: mechanism, prevention, return to play

Selected reading:

• Brody, H., Cross, R., & Lindsey, C. (2002). The Physics and Technology of Tennis. Racquet Tech Publishing.
• Cross, R. (2000). The dead spot of a tennis racquet. American Journal of Physics.
• Knudson, D. (2014). Biomechanical Principles of Tennis Technique: Using Science to Improve Your Strokes. Racquet Tech Publishing.