Most strings are made of nylon, in various gauges/thicknesses. The thicker the string, the more durable. So, for those tennis players who break strings regularly, they may start out with a 17 gauge/1.25mm string, move on to a 16 gauge/1.30mm and end up on a 15 gauge 1.35mm. Some may want to keep on using the softer nylon (also known as synthetic gut) and move to a 14 gauge/1.42mm which is hard to find these days.
Synthetic gut strings can be divided into two groups – SINGLE CORE or MULTIFILAMENT.
Single core has just one central core of nylon and when it wears the complete string will shear.
Multifilament’s have a core made up of many fibres that add arm comfort and more elasticity. They will gradually wear away over time and the fibres will start to peel away and look noticeably worn.
Polyester strings are designed for durability. Used for tennis only, good for those who find that the synthetic gut strings just break too soon. However, these very stiff strings produce added shock and vibration, so do not use for juniors or elderly players whose arm muscles and tendons will suffer.
For chronic string breakers, best to move up to a thicker synthetic gut/nylon and then if that still does not help, consider moving to a polyester string, but only for either the mains (usually) or the crosses, whichever is breaking. Many hard hitters end up moving from a thick gauge synthetic gut to a THIN gauge polyester and then hopefully not forced to increase the string gauge further. It’s common to see a poly string used for the mains only and a softer synthetic gut used for the crosses, to add a little more elasticity and arm comfort. If switching to a poly string, drop the usual tension by around 5 lbs at least.
Remember, the thicker/stiffer the string, the LESS power and elasticity and arm comfort. Poly strings are a common string choice for clay courts where the clay chews up the softer nylon.
TIGHT for control, LOOSE for power. Strings are always losing their tension, so a perfect tension will not last beyond two matches. Though the average club player may not notice the difference and will only ask for a restring when the strings break.
In WARM weather, tensions need to be a little higher as the ball will be moving faster. In COLDER weather, the ball moves slower and so a drop in tension will help produce more of a trampoline effect and a faster moving ball.
A thought about spin.
You will see many strings APPARENTLY claiming that their strings add more top spin/ball rotation. If you read closely, you will note that they only claim to ENHANCE or IMPROVE the spin. The fact is that it is ONLY the players actions that will result in more spin. The faster that the racket head meets the ball, the more potential for increasing ball rotation. It’s why polyester strings are related to Raf Nadal type top spin. Poly strings are LESS elastic, so the ball will drop short in court. To get the ball to the same depth, the player needs to swing the racket faster into the ball and it’s this increased racket head speed that will also increase ball rotation.