The natural continuation of this series is the topic of string. Of course no racquet will perform without string installed but the string and installation will make the performance suit the player.
Suiting the player is sometimes overlooked in favor of simply selecting a string based on marketing, peer usage, or stringer recommendation. If I were to rely on any one of the deciding factors it would be the “stringer”. Why? Typically the stringer will be up to speed with new products, their benefit(s), their issues, and what value is offered by this string.
Probably the most popular string material currently is polyester. You may hear this called co-poly, soft poly, or any number of similar modifiers. It is really difficult to nail down the “properties” of polyester strings because there are so many additives, but one thing we know is that polyester based string(s) are not very stable. That means they will lose tension quickly. This may be the reason that professional players change racquets at each ball change.
Another characteristic we know is that polyester based strings are very stiff in tension. This in itself is not horrible but the fact that these strings become “stiffer” as the ball is hit harder may create potential wrist, elbow and shoulder issues. This is the reason I will never recommend a polyester string for beginners or young juniors. There is just too much risk of repetitive use injuries. To be sure a string bed of 100% polyester may have a lower ASPS (Absolute String Plane Stiffness) than a good multi-filament but the multi-filament will absorb shock better as impact increases.
Another deciding factor is value. There are some really inexpensive polyester based strings available. This alone may make your selection easier but remember you get what you pay for, mostly! Many will notice that polyester based string is more durable than other materials but that does not necessarily relate to performance. While performance is difficult to quantify, failure is not. A broken string is a broken string, period. So, if your primary consideration is how long the string is in the racquet, and nothing else, you may prefer polyester.
However, if you value performance you need to look into other materials. It has long been agreed that natural gut is the best material for racquet string, but, it is very expensive compared to other materials. If cost is no object then use natural gut, period.
You may not want to hear this but nylon, yes nylon, has been the preferred material for racquet string for decades, and many would say is still the best overall material for value and performance. Of course there are a zillion strings available made from nylon but the ones we want to consider for performance are multi-filament construction. By using several different fibers internally the string can be designed to accomplish many things.
The construction can provide durability, elongation, gauge, bonding agents, and abrasion resistance. The more components used in a string the more it will cost. Here is where you need to decide what is important to you. A good multi-filament string will perform really well for about 25 hours. The string will probably be in the racquet much longer than that but best performance will be experienced in the first 20 to 25 hours.
In summary, then, I prefer multi-filaments for ninety (90%) of my adult clients and one hundred (100%) of my junior clients. There are of course mitigating factors and these should be considered but the prime consideration is making sure the player can continue to play and does not experience discomfort or injury.