Why do tennis strings lose tension, and what can you do about it?

In short: a string loses tension because it is made of a viscoelastic material that relaxes as soon as it is tensioned, and with every hit. The loss is fastest in the first few days (around 13% for a polyester and a synthetic in a 21-day test on unplayed rackets), and heat makes it worse: leaving your racket in a hot car is one of the worst cases measured. Good news: according to Tennis Warehouse University's measurements, ball speed drops only 1 to 3 mph in normal play. What you mostly notice is a string that feels stiffer and less lively.

What happens inside the string

A tennis string is a viscoelastic polymer: partly elastic (it returns to its length after each hit), partly viscous (its long molecular chains slowly slide past each other). When a racket is strung, the string is stretched and then clamped at a fixed length. It no longer lengthens, but the force it exerts gradually falls, because its chains rearrange toward a less tense state. Researchers call this stress relaxation; players call it tension loss.

According to Tennis Warehouse University, this phenomenon starts as soon as the racket is strung and continues with every hit. So it isn't a sign of a faulty string or a poor job: it's the nature of the material itself.

A fast loss in the first few days

The manufacturer Ashaway publishes a test by stringer John Gugel (Racquet Quest): three strings tensioned at 60 lb (about 27 kg) on identical rackets, stored under stable conditions and never played, with tension measured over 21 days.

Read this with caution: the test is published by a manufacturer promoting its own product, and covers a single string per family. It gives an order of magnitude, not a rule. It also shows that the polyester tested regained a little tension until day eight before losing it fairly quickly, and was the least consistent of the three. You'll find online estimates of 10 to 25% loss in the first 24 hours, but with no measurement cited: we don't repeat them.

The factors that speed up the loss

• The material : Tennis Warehouse University says the loss depends heavily on the material, with gut, then nylon, then polyester losing the least, in that order. The Ashaway test qualifies that ranking (the nylon tested lost more than the polyester after 21 days): don't take any ranking as absolute. Tennis Warehouse Europe, for its part, describes monofilament as tending to lose tension quickly and multifilament as holding tension very well.
• Moisture : Ashaway points out that nylon is hygroscopic: it absorbs moisture, which hurts tension maintenance.
• Heat after stringing : in Tennis Warehouse University's temperature study, the most marked effect is that exposure to high heat after stringing, such as leaving the racket in a car in summer, produces the greatest drop in tension. That exposure matters more than heat during stringing. Conversely, cold strings play stiffer and hot strings play softer.
• Play : each hit adds to the string's relaxation, on top of the loss that happens without playing.
• The stringing machine : according to Wikipedia, lockout machines allow more tension loss than drop weight or constant pull machines, which account for the string stretching.
• Pre-stretching : Tennis Warehouse University observes that a pre-stretched string gains stiffness and energy return, with a shorter dwell time and less deflection. Ask your stringer whether they pre-stretch.

On choosing the machine and the questions to ask a stringer: how to choose a tennis stringer.

What it really changes about your game

In its measurements on a polyester string hit until its tension fell, Tennis Warehouse University concludes that in normal play you can only expect a 1 to 3 mph difference in ball speed. The loss of raw power is therefore small. What players experience as a “dead” string comes rather from several combined effects: more friction between strings, decreasing stiffness, a longer dwell time and falling tension. The result feels like a stiffer, less responsive string.

That doesn't contradict Tennis Warehouse Europe, which notes that a string that has lost tension has also lost playability, so power, control and feel: raw power varies little, but the feel changes clearly. From the trade, RacquetTECH offers a benchmark: a string that has lost 25 to 30% of its original tension should be replaced, even if it isn't broken.

To know when to replace your strings: when should you restring your tennis racket. To choose your starting tension: what tension should you choose for your tennis racket.

How to limit the loss, and what you can't avoid

• Don't leave your racket in a hot car : it's the most avoidable factor, and according to the measurements one of the most penalising.
• Ask your stringer the right questions : machine type, pre-stretching, ability to measure the tension loss in your current strings.
• Accept the loss of the first few days : it's normal: the real tension of your racket is lower than the stringing tension in the days after, whatever the string.
• Choose a string that suits your rhythm : a string that holds tension better isn't always the one that lasts longest: see the monofilament and multifilament comparison.

To compare string families on this criterion: monofilament or multifilament and, if you're considering a mixed setup, hybrid tennis strings: how to choose, fit and tension them.

Keeping track of your setup

Knowing whether your strings have lost too much tension means remembering the date of the last restring, the string used and the tension it was strung at, especially with several rackets. That rarely happens.

That's exactly what Tension wants to make easier: keeping the history of your restrings (date, string, tension) so you no longer have to remember, and finding an available stringer near you. Tension is coming to Belgium in late 2026, and you can already get notified at launch.

Are you a stringer or a shop? Tension Pro is designed to manage your orders, customers and stringing jobs, while letting new players find and book you. For the big picture, see our tennis stringing guide.