MaterialsInMotion

As I was scrolling through YouTube instead of working on college applications, I came across this video by PongGenius titled “How Table Tennis Blades ACTUALLY Work.” This was a topic that I was already curious about. While I could somewhat wrap my head around the physics of table tennis rubbers on my own (since they are what directly contact the ball), I could never do the same for blades (the wooden core of all table tennis paddles). Thus, I decided to give the video a watch.

The video first defines two key characteristics of wood: hardness and elasticity. Hardness determines the distribution of the force applied by the ball onto the surface of the blade. A softer wood will create a dent under the spot that the ball contacts to cushion the ball and give more time for the player to influence the trajectory of the ball, often referred to as dwell time. On the other hand, a harder wood resists creating this dent and instead evenly distributes the force from the ball across the blade’s surface, which creates a more consistent bounce in a bigger area on the paddle (called the sweet spot) but in turn gives the player less dwell time.

Elasticity is the wood’s ability to store and return energy upon impact, or its ability to return to its original shape after deforming from the ball’s impact. A more elastic wood snaps back after impact and sends the ball away with more speed, while a less elastic wood absorbs the ball’s energy and offers more control. PongGenius also mentions that these two characteristics often go hand-in-hand: harder woods tend to be more elastic, and softer woods tend to be less elastic. This observation is just a general trend, though.

The video then segways into discussions of blade composition. Most all-wood blades follow a five-ply or seven-ply composition with one main pattern: the core is almost always made of the softest wood, and the type of wood used becomes harder as the layers approach the surface of the blade. Within this pattern are three smaller categories that he called the smooth gradient, the steep gradient, and the geared blade. The smooth gradient describes blades whose layers do not have drastic jumps in hardness and are the most controlled and forgiving type of the three. The steep gradient is the exact opposite—its layers drastically increase in hardness, creating a “best of both worlds” situation in which the hard outer layer can provide speed and power, while the soft core still provides cushion and control. The geared blade differs greatly from the other two categories because the hardest layer is sandwiched between the outer ply and the core. This composition allows for high control on slower shots because the ball only sinks into the outer layer while still giving good power for stronger shots in which the ball can sink into the harder ply, hence the different “gears” like those in cars.

PongGenius then introduces what many consider the most complicated aspect to consider when purchasing a blade: composite materials. In his video, he only focused on carbon, which can be used alone or woven with different fibers to create different effects. He explained that manufacturers can only add so many wood layers before blades become heavy and difficult to use, so they began implementing thin layers of carbon that added “enormous stiffness and elasticity at almost no weight cost.” However, the location of the carbon layer within the blade changes how it behaves, and two main approaches dominate the market. Outer carbon, also referred to as outer-layer or outer-force, is the placement of the carbon layer directly below the surface wood ply. This placement allows for the engagement of the carbon layer in every shot and is best suited for aggressive players who are willing to sacrifice some control on softer shots. Inner carbon, also known as inner-layer or inner-force, places the carbon layer directly above the core and creates a more extreme geared blade feeling.

It never occurred that carbon was introduced into table tennis blades for similar reasons as in metal production. I always took carbon blades at their surface level—that they were simply faster than all-wood ones. However, after watching this video, I feel like I can apply my newfound knowledge to the various fibers that are also used in blades. Those that are advertised as having a large sweet spot are likely harder, while those that advertise more spin and control are likely softer. The new “super carbon fibers” that are more tightly woven than previous ones are likely harder and more elastic to create their stronger catapult effect. However, so many fibers exist on the market. How many of them are basically the same thing? How many of them are drastically different? Why do manufacturers specialize in the ones that they picked?