❄️ The short version
- Outdoors in the cold: string lower. A cold string is stiffer. Tennis Warehouse University (TWU) advises stringing "lower for cold".
- Indoors: go back up. Tecnifibre advises taking 1 kg (about 2 lb) off outdoors and putting it back indoors, where the ball plays faster.
- By how much? No measurement gives it in pounds or kilos. The only published figure, 1 kg, is a manufacturer's advice.
- Polyester and cold: only one polyester was measured at 0 °C (32 °F). That is too few to conclude anything.
In autumn, some players stay outdoors while others move indoors. Same question for everyone — should you change your tension? — and two opposite answers.
🧊 1. What TWU Measured Between 0 and 20 °C
In June 2016, Crawford Lindsey (Tennis Warehouse) and Rod Cross (University of Sydney) measured string stiffness at 0, 20 and 40 °C (32, 68 and 104 °F). Each string is clamped on its own between two grips; 0 °C is reached with crushed ice. What is measured is therefore the lengthwise stiffness of a single string, not that of a strung bed.
The result: the colder it is, the stiffer the string, even if the effect "is not great". Only seven strings have a 0 °C value in the published table:
| String tested | Material (Table 1) | Stiffness change, 0 to 20 °C |
|---|---|---|
| Luxilon Alu Power 1.38 | Polyester | −10.9% |
| Ashaway Crossfire 1.25 | Kevlar | −6.5% |
| Volkl V-Torque 1.18 | Nylon (see § 2) | −5.2% |
| Wilson Optimus 1.30 | Nylon | −4.8% |
| Wilson NXT Duramax 1.40 | Nylon | −2.1% |
| Wilson Natural Gut | Gut | −2.0% |
| Head FXP Tour 1.30 | Nylon | +4.8% |
Source: Tennis Warehouse University, "The Effect of Temperature on Tennis String Tension and Stiffness", Table 1, June 6, 2016. A negative change means the string is less stiff at 20 °C than at 0 °C, so stiffer in the cold.
Six strings out of seven are stiffer at 0 °C; the Head FXP Tour does the opposite. TWU's advice: "string lower for cold and higher for hot on-court temperatures". Heat is covered in our article on tennis strings and heat; here is the other half of the sentence.
How many pounds? TWU does not convert its percentages, and neither do we. The same page points out that tension tells you about stiffness only when comparing the same string at different tensions, not different strings with each other.
🔬 2. Polyester and the Cold: One String Measured
The table seems to confirm the received idea: Alu Power, the only string labelled polyester, shows the largest change (−10.9%). Three caveats stop us from turning it into a rule.
- One polyester. A measurement on one string says nothing about a family.
- The V-Torque changes label: "polyester" in the sample list, "nylon" in Table 1 of the same publication.
- TWU contradicts itself. Its text judges gut and nylon "more sensitive to temperature than did the polyester and kevlar strings"; its table puts gut at −2.0% and polyester at −10.9%.
Another internal disagreement: the text says strings 8 to 15 were not measured at 0 °C, with no. 7 (V-Torque) the only exception. Yet the table gives 0 °C values for nos. 8, 10, 11, 12 and 13, and the positive change belongs to no. 8 (FXP Tour). We reproduce the published table and flag the disagreement.
🏭 3. What Tecnifibre Says, and How to Read It
Tecnifibre, in its Tecnimag magazine (April 30, 2025), our translation: "Gut, for example, suffers little from the weather, as does multifilament, whereas polyesters suffer more from cold temperatures. Stiff string + stiff ball when it is cold = difficulty getting the ball to travel, so it can be worth lowering the tension."
Same direction as TWU: in the cold, go lower. Two precautions, though. It is advice without a measurement. And it comes from a manufacturer that sells multifilaments: that does not make it wrong, only unverified.
🏟️ 4. Indoors: the Opposite Correction
This is where the two winters part ways. The same page writes, again in our translation: "outdoors, the wind […] and the sun […] will push you to lower your tension […]. We would advise you to lower the tension by 1 kg. Indoors, you add that kilo back."
The reason is not thermal; it is the ball. Tecnifibre explains that on indoor hard courts "the felt disappears, the ball becomes smoother over time and is therefore lighter and faster". A livelier ball calls for control. Our tension guide already gave this direction of correction; here is its source.
One piece of data is missing: the temperature of a heated indoor hall is documented by neither source, nor by any other we found. The indoor correction rests on the ball, not on the thermometer.
💡 Expert point — Tecnifibre's kilo is relative. Tecnifibre does not say "+1 kg above your usual tension". It says: take 1 kg off outdoors, put it back indoors. If you only play indoors, nothing suggests stringing tighter than your reference.
✅ 5. The Protocol, in Three Cases
You play outdoors, in the cold
Go lower, starting with 1 kg (about 2 lb): Tecnifibre's order of magnitude, to be taken as a first trial, not as a measurement. Lowering tension also reduces the firmness of the stringbed: for a sensitive arm, it is the risk-free direction.
You play indoors
Go back to your reference tension. With a sensitive arm or a history of tennis elbow, do not go above it to gain control: changing to a softer string does more for your arm than any tension tweak.
You alternate
Two racquets, same string: one at your reference for indoors, the other 1 kg lower for outdoors. With a single racquet, string for the place where you play most.
In all three cases, the configurator shows what that kilo changes to your setup's firmness index. It does not simulate temperature, only tension: precisely the variable you are changing. To soften through the string rather than the tension, every page of the string catalogue gives its stiffness.
❄️ See what −1 kg does to your firmness index
Enter your frame, your string and your tension, then run the calculation again with one kilo less.
Compute my RCS index →❓ FAQ — String Tension in Winter
Should you lower your string tension in winter?
Outdoors, yes: a cold string is stiffer, and Tennis Warehouse University advises stringing lower for the cold. Indoors, no: Tecnifibre advises adding back the kilo you took off outdoors, because the ball plays livelier there.
How much should I lower my tension when it is cold?
No measurement gives it in pounds or kilos. The only published figure is Tecnifibre's advice: 1 kg (about 2 lb) less outdoors, to be treated as a first trial.
Is polyester more sensitive to the cold?
That is not established. Tecnifibre says so; at TWU, a single polyester was measured at 0 °C (−10.9% stiffness between 0 and 20 °C), and the study's own text judges gut and nylon more temperature-sensitive than polyester.