What is a "Carbon" layer?

Well, it starts with the fact that a carbon layer, isn't necessarily a carbon layer. The term has been used generically to describe a composite layer in a blade, but it really refers to just one specific type of fiber, i.e., Carbon-fiber. The reason is probably because Carbon was one of the first fibers used in TT blades, but many others have been introduced since then. So, I'm going to make a little breakdown about this subject, and hopefully help people in using the correct term - composite layer.

So, why is it called a composite layer after all? It's called this way because it is composed of two, or more materials. In essence, carbon or other fibers, are just fabrics, they are very flexible in their natural form, if you just glue them in a blade like that they will just be dead weight. To really bring out their characteristics, they need a matrix to bond the fibers to themselves, this process is called lamination. That matrix is usually a resin. So, a composite layer = fabric + resin. True, there are some special cases like CNF where it’s just one material, but in reality no, because CNF is essentially wood fibers in a PVA matrix, so the logic still applies. Here is where the challenge begins, because apart from the several different types of existing fabrics, we also have a gazillion types of resin on the market. This lamination process is very important and can greatly affect how the blade feels, a very simple example would be the commercial version of the HL5 vs the national version. There are a lot of variables that make this a complex process: resin type, resin amount, curing temperature, curing speed, pressure… So even if the same fabric is used, different results can be achieved if we play with the other variables. Big brands have this process standardized, and it’s roughly the same for their models, but it can be slightly different from brand to brand. In fact, I've seen that big "B" press their blades in big piles, all at the same time. This causes the blades from the extremities of the pile to have more pressure than the ones in the center, due to material deformation, so the feeling of those blades might be slightly different as well. As you can see, even blades from the same model may feel different, blades with similar composition from different brands feel different, and it's also another reason why making “clone” blades is such a difficult task.

In terms of fabrics, we also have different types. The three main characteristics that define a fabric are: fabric type, weave type, and density.

Fabric type

It refers to the individual fibers that compose the fabric, it can be split into two categories:

Plain Fabric: Is composed of only one type of fiber. Popular examples would be Carbon (carbon-fiber), ZLF (Zylon-fiber), Al (Arylate - fiber)...

Hybrid Fabric: Is composed of two or more different fibers, usually the name refers to the specific fibers being used. Your typical ALC for example, uses Arylate fibers and Carbon fibers.

Weave type

It refers to how the fibers are interlocked to form the fabric, it can also be split into two categories, non-woven and woven.

Non-woven fabrics: Also called fleece, the fibers don’t have a specific direction in the fabric, they are random. Your most common example would be soft-carbon, or fleece-carbon. Because the position of the fibers is random, they don’t offer an increase in mechanical properties in any specific direction, unlike woven fabrics.

Woven fabrics: This is your most popular type of fabric, the fibers are interlocked in specific patterns. Think of them as strings on a tennis racquet, you have vertical strings and horizontal strings. In tennis, players adjust the type and tension of the strings to better fit their needs. In TT we can’t adjust the tension, but we can change the type of fiber. Vertical fibers have a big impact on the stiffness of the blade, while the horizontal fibers have a greater impact on the hardness (and feeling) of the blade. For plain fabrics, the weave type is not that important, because it’s just the same fiber in both directions.

With Hybrid fabrics it’s a different story, because you can combine those fibers in many different ways, and consequently affect stiffness and hardness differently. Plain weave is the simplest and most common type, where the yarns cross over and under each other at right angles, but the choice of fiber in each thread, will decide the fabric’s performance. Here are a few examples:

Plain weave - here we have Aramid and carbon fiber in a 1:1 ratio in both directions. The ratio refers to the amount of fibers that exist in that fabric, which in this case is the same for both.

We can also change the ratio of the fibers, for example with my AC-I we have a ratio of 2:1, meaning that we have twice the amount of fiber than the other, in each direction. In the picture below you can see that horizontally we have two Aramid threads for one Carbon thread, but vertically we have 1 Aramid thread for 2 Carbon threads. This forms an “I” pattern, hence the name AC-I.

We can also choose to have just one fiber in each direction. In the next picture you can see my Ax-C, it only has Aramid horizontally (x direction), and carbon vertically. With these types of fabrics we are addressing the stiffness and hardness of the blade more directly, by choosing to maximize those properties using specific fibers. We maximize the stiffness by using a very stiff fiber vertically (carbon), and we keep the softness of the blade by using a relatively soft fiber horizontally (Aramid).

Of course the opposite can also be used, if you want a more flexible but harder blade. By rotating the fabric we get Ay-C.

Density

I often hear people referring to fabrics by thickness, but that’s not correct. The thickness is a consequence of the weave type (and specific fibers being used), of course that is also something important to keep in mind because the ITTF only allows a maximum of 0.35mm for composite layers.

Usually we refer to fabrics by their density, a greater density is achieved by having more thread in the fabrics, meaning that they are more closely woven, but also heavier. The weight of the specific fibers being used matters as well, these fibers don’t have all the same weight. For example, one of the advantages of Zylon is that it has high mechanical properties with lower weight, this way we can achieve a more tightly woven fabric with a similar density.

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