FAQ about tennis balls and tennis racket strings

RS Tennis is working to develop the most premium products you can get in each of our segments. We are working with the finest materials and components to secure our quality.

We often get questions from our fans how tennis balls are made and what different materials they are composed by. The same goes for tennis racket strings and the broad audience of the tennis population don´t really know the processes behind the development of tennis balls and tennis racket strings.

Here are some FAQs regarding tennis balls and tennis racket strings: 


What is a tennis ball made of?

Today's tennis balls are made of a hollow, two-piece rubber shell filled with pressurized gas. The rubber shell is covered with felt made from nylon or wool. The International tennis federation, ITF states that tennis balls should be between 2 1/2 and 2 5/8 inches in diameter and weigh between 2 and 2 1/16 oz. The felt used to cover tennis balls destined for official play is bright yellow.

RS is only working with the finest felt types available on the market.

Balls which haven't got enough pressure inside make a thud when they hit the floor. These are called dead balls.

How are tennis balls made?

RS Tennis and other tennis ball manufacturers mold rubber into two shapes that are pressed together to form the core of a ball. To achieve an appropriate level of bounciness, tennis ball makers inject a specific amount of pressurized air into the center of each rubber core. Manufacturers buff the sealed, pressurized rubber balls and cover them in glue. Machines cut long pieces of bright yellow felt into two shapes that are wrapped around each tennis ball to form a covering. Ball makers heat the completed tennis balls to make the glue form a seal that holds the two pieces of fabric together.

Bounce of a tennis ball?

The ITF states that tennis balls must bounce between 53 and 58 inches high after being dropped onto a concrete floor from an elevation of 100 inches. To achieve this precise bouncing height, tennis ball makers add a very specific amount of air to the core of tennis balls. In general, tennis balls are pressurized to 12 pounds per square inch.



What materials are there in a tennis racket string?

There are many different types of strings on the market. They differ in terms of material. Below we have summarized the different types of strings and materials.

(Thanks to Tennis Warehouse for part of the answers) 

Nylon - synthetic gut or nylon? Truth be told, most synthetic guts are made with nylon (sometimes referred to as polyamides). There are different grades of nylon, with varying levels of feel, so don't be afraid to try different synthetic guts until you find the right fit. All in all, synthetic gut delivers a good combination of playability and durability at a great price. In the old days (wood racquet era), any self-respecting player used natural gut. Today, an impressive number of non-professional players use nylon-based strings, which have greatly improved in the feel department. In fact, Nylon multifilaments offer truly impressive comfort and power. Unlike the more basic synthetic guts (which have a single, solid core), multifilaments are comprised of hundreds or thousands of ultra pliable, elbow-friendly fibers, and bundled together with flexible resins like polyurethane. Other string materials include:

Natural Gut - the ultimate in playability, feel and tension maintenance. Often overlooked due to it's cost, natural gut is the best choice for players with arm problems or those who crave its sublime, comfortably crisp feel. Formerly, the number one choice of ATP and WTA tour players. Now used more in hybrids, combining polyester mains with natural gut crosses (with some players using gut in the mains for more power and feel). Natural gut offers maximum feel and control due to its ultra low stiffness, which provides phenomenal ball "pocketing".

Polyester- a very durable string designed to provide control and durability to players with long, fast strokes. Polyester is the number one choice on the pro tour because it allows advanced ball strikers to maintain surgical control on their fastest, most aggressive strokes. The incredible stroke speed enabled by polyester also translated into categorically higher level of spin, which literally changed the trajectories and angles available to the player. Polyester also served to harness the immense power that came with graphite era. While it used to be too stiff and dead for recreational players, a growing number of string manufacturers have devoted the lion's share of their R&D to creating softer, more elastic polys so that a wider cross section of players can enjoy its benefits. Another way to get the benefits of polyester is through a hybrid, also very popular on the pro tour. This is typically done by combining polyester (usually in the mains) with natural gut or multifilament crosses. This setup provides the durability, control and spin of polyester with the comfort, power and touch of a softer string - otherwise known as the best of both worlds. Due to its high stiffness and relatively low power, polyester is not recommended for beginners or players with arm injuries.

Kevlar - The most durable string available. Kevlar is very stiff and strings up very tight. Therefore, it is usually combined with a soft nylon cross to reduce string bed stiffness. Ultimately, Kevlar hybrids are the least powerful and least comfortable strings currently available. Players trying kevlar hybrids for the first time (from nylon strings) are recommended to reduce tension by 10% to compensate for the added stiffness. Not recommended for beginners or players with arm injuries.



String tension is the final piece in the racquet-string-tension triad. It's also the least understood by most recreational players. Let's start with the basics - lower tensions provide more power, tighter tensions provide more control. This is a very general rule of thumb and assumes a certain level of player ability (especially the control part). A beginning player may need more control but tighter string tensions aren't the solution. This player needs a soft, forgiving stringbed that lower tensions provide due to the frequency of off-center hits. Advanced players who swing fast and hit hard usually need more control and will, therefore, benefit from tighter tensions. There are, of course, always exceptions but these generalizations apply to the majority of players.

Each racquet has a recommended tension range. This range has been determined by the manufacturer as a result of extensive playtesting by real players. If a player doesn't have a specific need (more power, arm problems, etc.), he should start at mid-range and make any adjustments from there.

Otherwise, here are some specific guidelines for selecting a string tension.


As we stated above, if a player is seeking more power from his racquet, he should try dropping tension a few pounds. The stringbed will deflect more (and the ball less), returning greater energy to the ball. There is a point of diminishing returns where the stringbed turns into a butterfly net, but it's well below any racquet's recommended tension range.


A tighter stringbed deflects less and deforms the ball more, providing less energy than looser strings. This means the ball won't fly as far when you hit it. Beginners who are shanking the ball in every direction won't gain any advantage by increasing tension, but intermediate and advanced players who are hitting a lot of long balls will be able to reduce the depth of their shots without changing their swing. It is also generally accepted that spin potential is enhanced with higher tensions, which provides even more control for topspin and slice players.

Arm Injuries - lower tensions result in a softer stringbed and a larger sweetspot, reducing the amount of shock and vibration transmitted to the hand and elbow.

Switching Racquets - too many players are stuck on a tension ("I always string my racquet at 60 pounds") and don't make allowances when changing racquets. Whether changing head sizes, brands, or buying a new titanium racquet, a player will need to make the corresponding tension change. If 60 pounds was mid-range on his old racquet and the new racquet's tension range is 50-60 pounds he should start at 55 pounds with the new racquet.

Switching Strings - if a player changes from a soft string (natural gut, syn gut, multi) to a poly-based string, we suggest reducing tension 5-10% to compensate for the higher stiffness. This is more art than science and may require trial and error to get the feel exactly right. When switching to Kevlar be advised that this material is much stiffer than nylon synthetics and quite a bit stiffer than most ploy-based strings - so tension accordingly.


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